preboot: Introduce CONFIG_USE_PREBOOT and migrate CONFIG_PREBOOT

This is the same migration path as commit b6251db8c3 ("Kconfig:
Introduce USE_BOOTCOMMAND and migrate BOOTCOMMAND").

I also moved the description in README to the Kconfig help.
I ripped off the sentence about 'LWMON' since it is gone already.

I only let my boards migrate, leaving the rest to platform maintainers.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

README

@@ -687,22 +687,6 @@ The following options need to be configured:
 		as a convenience, when switching between booting from
 		RAM and NFS.
 
-- Pre-Boot Commands:
-		CONFIG_PREBOOT
-
-		When this option is #defined, the existence of the
-		environment variable "preboot" will be checked
-		immediately before starting the CONFIG_BOOTDELAY
-		countdown and/or running the auto-boot command resp.
-		entering interactive mode.
-
-		This feature is especially useful when "preboot" is
-		automatically generated or modified. For an example
-		see the LWMON board specific code: here "preboot" is
-		modified when the user holds down a certain
-		combination of keys on the (special) keyboard when
-		booting the systems
-
 - Serial Download Echo Mode:
 		CONFIG_LOADS_ECHO
 		If defined to 1, all characters received during a

common/Kconfig

@@ -232,6 +232,24 @@ config BOOTCOMMAND
 	  This is the string of commands that will be used as bootcmd and if
 	  AUTOBOOT is set, automatically run.
 
+config USE_PREBOOT
+	bool "Enable preboot"
+	help
+	  When this option is enabled, the existence of the environment
+	  variable "preboot" will be checked immediately before starting the
+	  CONFIG_BOOTDELAY countdown and/or running the auto-boot command resp.
+	  entering interactive mode.
+
+	  This feature is especially useful when "preboot" is automatically
+	  generated or modified. For example, the boot code can modify the
+	  "preboot" when a user holds down a certain combination of keys.
+
+config PREBOOT
+	string "preboot default value"
+	depends on USE_PREBOOT
+	help
+	  This is the default of "preboot" environment variable.
+
 menu "Console"
 
 config MENU

configs/uniphier_ld4_sld8_defconfig

@@ -10,6 +10,8 @@ CONFIG_MICRO_SUPPORT_CARD=y
 CONFIG_NR_DRAM_BANKS=3
 # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set
 CONFIG_BOOTCOMMAND="run ${bootdev}script; run ${bootdev}boot"
+CONFIG_USE_PREBOOT=y
+CONFIG_PREBOOT="env exist ${bootdev}preboot && run ${bootdev}preboot"
 CONFIG_LOGLEVEL=6
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_NOR_SUPPORT=y

configs/uniphier_v7_defconfig

@@ -9,6 +9,8 @@ CONFIG_MICRO_SUPPORT_CARD=y
 CONFIG_NR_DRAM_BANKS=3
 # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set
 CONFIG_BOOTCOMMAND="run ${bootdev}script; run ${bootdev}boot"
+CONFIG_USE_PREBOOT=y
+CONFIG_PREBOOT="env exist ${bootdev}preboot && run ${bootdev}preboot"
 CONFIG_LOGLEVEL=6
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_NOR_SUPPORT=y

configs/uniphier_v8_defconfig

@@ -8,6 +8,8 @@ CONFIG_MICRO_SUPPORT_CARD=y
 CONFIG_NR_DRAM_BANKS=3
 # CONFIG_ARCH_FIXUP_FDT_MEMORY is not set
 CONFIG_BOOTCOMMAND="run ${bootdev}script; run ${bootdev}boot"
+CONFIG_USE_PREBOOT=y
+CONFIG_PREBOOT="env exist ${bootdev}preboot && run ${bootdev}preboot"
 CONFIG_LOGLEVEL=6
 CONFIG_CMD_CONFIG=y
 CONFIG_CMD_IMLS=y

include/configs/uniphier.h

@@ -124,8 +124,6 @@
 	"third_image=u-boot.bin\0"
 #endif
 
-#define CONFIG_PREBOOT			"env exist ${bootdev}preboot && run ${bootdev}preboot"
-
 #define CONFIG_ROOTPATH			"/nfs/root/path"
 #define CONFIG_NFSBOOTCOMMAND						\
 	"setenv bootargs $bootargs root=/dev/nfs rw "			\