armv7: Prevent CBFS data overlapping bootblock.

For arm/snow, current bootblock is larger than previously assigned CBFS offset
and will fail to boot. To prevent this happening again in future, cbfstool now
checks if CBFS will overlap bootblock.

A sample error message:
	E: Bootblock (0x0+0x71d4) overlap CBFS data (0x5000)
	E: Failed to create build/coreboot.pre1.tmp.

arm/snow offset is also enlarged and moved to Kconfig variable.

Change-Id: I4556aef27ff716556040312ae8ccb78078abc82d
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: http://review.coreboot.org/2295
Tested-by: build bot (Jenkins)
Reviewed-by: David Hendricks <dhendrix@chromium.org>

src/cpu/samsung/exynos5250/Kconfig

@@ -48,6 +48,11 @@ config ROMSTAGE_SIZE
 	hex
 	default 0x10000
 
+config CBFS_ROM_OFFSET
+	# Calculated by BL1 + max bootblock size.
+	hex "offset of CBFS data in ROM"
+	default 0x0A000
+
 # TODO Change this to some better address not overlapping bootblock when
 # cbfstool supports creating header in arbitrary location.
 config CBFS_HEADER_ROM_OFFSET