armv7/snow: add BL1_SIZE_KB and get rid of magic constants

This adds a BL1_SIZE_KB config variable so that we can get rid of
some magic constants.

Change-Id: I9dbcfb407d3f8e367be5d943e95b032ce88b0ad0
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/2332
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/cpu/samsung/exynos5250/Kconfig

@@ -14,6 +14,10 @@ config SATA_AHCI
 	bool
 	default n
 
+config BL1_SIZE_KB
+	int
+	default 8192
+
 # Example SRAM/iRAM map for Exynos5250 platform:
 #
 # 0x0202_0000: vendor-provided BL1