ARM: Make it possible to use a custom bootblock implementation.

Tegra needs to use a custom bootblock implementation because it starts on a
coprocessor which uses ARMv4. It doesn't have the same control registers,
caches, etc., and the regular bootblock gets exceptions and dies.

Change-Id: Id197db2939bc840ad64244d6e2017fc5c89e0cbd
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/171018
Reviewed-by: Ronald Minnich <rminnich@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit a66393fdd6)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6710
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/arch/armv7/Kconfig

@@ -11,6 +11,12 @@ config ARCH_RAMSTAGE_ARMV7
 	bool
 	default n
 
+# If a custom bootblock is necessary, this option should be "select"-ed by
+# the thing that needs it, probably the CPU.
+config ARM_BOOTBLOCK_CUSTOM
+	bool
+	default n
+
 config CPU_HAS_BOOTBLOCK_INIT
 	bool
 	default n

src/arch/armv7/Makefile.inc

@@ -51,11 +51,12 @@ endif # CONFIG_ARCH_ARMV7
 
 ifeq ($(CONFIG_ARCH_BOOTBLOCK_ARMV7),y)
 
-bootblock-y += id.S
+ifneq ($(CONFIG_ARM_BOOTBLOCK_CUSTOM),y)
 bootblock-y += bootblock.S
-
+bootblock-$(CONFIG_BOOTBLOCK_SIMPLE) += bootblock_simple.c
+endif
+bootblock-y += id.S
 $(obj)/arch/arm/id.bootblock.o: $(obj)/build.h
-bootblock-y += $(call strip_quotes,$(CONFIG_BOOTBLOCK_SOURCE))
 
 bootblock-y += stages.c
 bootblock-y += cache.c