arm: Move CP15 init out of cpu_init_crit()

Some SOCs have do not start up with their 'main' CPU. The first U-Boot
code may then be executed with a CPU which does not have a CP15, or not a
useful one.

Here we split the initialization of CP15 into a separate call, which can
be performed later if required.

Once the main CPU is running, you should call cpu_init_cp15() to perform
this init as early as possible.

Existing ARMv7 boards which define CONFIG_SKIP_LOWLEVEL_INIT should not
need to change, this CP15 init is still skipped in that case. The only
impact for these boards is that the cpu_init_cp15() will be available
even if it is never used on these boards.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>

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

@@ -46,6 +46,9 @@ extern ulong IRQ_STACK_START_IN;	/* 8 bytes in IRQ stack */
 int	cpu_init(void);
 int	cleanup_before_linux(void);
 
+/* Set up ARMv7 MMU, caches and TLBs */
+void	cpu_init_cp15(void);
+
 /* cpu/.../arch/cpu.c */
 int	arch_cpu_init(void);
 int	arch_misc_init(void);