exynos5250: Implement support to boot with USB A-A firmware upload

This patch implements the basic infrastructure required to use the USB
A-A firmware upload feature on Exynos5 processors with Coreboot. It will
require a corresponding host-side script that activates the feature and
uploads the correct image parts in the correct order to harcoded target
addresses, as described in the comments of alternate_cbfs.c.

Also fixes a bug in the Google Snow mainboard where it would not
correctly initialize the pinmux configuration for the SPI flash bus.
During a normal SPI boot the IROM would already do that for you, but
when booting from USB you have to do it yourself.

Change-Id: I40a39f8f5d1d70b58dbf258015c1653a27097d67
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/64875
Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Reviewed-on: http://review.coreboot.org/4456
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/arch/armv7/bootblock_simple.c

@@ -55,9 +55,6 @@ void main(void)
 	/*
 	 * Re-enable icache and branch prediction. MMU and dcache will be
 	 * set up later.
-	 *
-	 * Note: If booting from USB, we need to disable branch prediction
-	 * before copying from USB into RAM (FIXME: why?)
 	 */
 	sctlr = read_sctlr();
 	sctlr |= SCTLR_Z | SCTLR_I;