armv7: replace magic constant for romstage location

This replaces 0x02023400 with an SoC-specific Kconfig variable.

Change-Id: I21482d54a1e1fa6c4437c030ddae2b0bb3331551
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/2130
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/arch/armv7/romstage.ld

@@ -39,8 +39,7 @@ ENTRY(_start)
 
 SECTIONS
 {
-	/* FIXME: replace this with CPU-specific Kconfig variable */
-	. = 0x02023400;	/* Exynos5 */
+	. = CONFIG_ROMSTAGE_BASE;
 
 	.romtext . : {
 		_rom = .;