sandbox: implement reset

Up to now the sandbox would shutdown upon a cold reset request. Instead it
should be reset.

In our coding we use static variables like LIST_HEAD(efi_obj_list). A reset
can occur at any time, e.g. via an UEFI binary calling the reset service.
The only safe way to return to an initial state is to relaunch the U-Boot
binary.

The reset implementation uses execv() to relaunch U-Boot.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/include/asm/u-boot-sandbox.h

@@ -84,6 +84,16 @@ void sandbox_set_enable_pci_map(int enable);
  */
 int sandbox_read_fdt_from_file(void);
 
+/**
+ * sandbox_reset() - reset sandbox
+ *
+ * This functions implements the cold reboot of the sandbox. It relaunches the
+ * U-Boot binary with the same command line parameters as the original call.
+ * The PID of the process stays the same. All file descriptors that have not
+ * been opened with O_CLOEXEC stay open including stdin, stdout, stderr.
+ */
+void sandbox_reset(void);
+
 /* Exit sandbox (quit U-Boot) */
 void sandbox_exit(void);