armv7: set CBFS header to zero

This is necessary to make sure that bootblock uses the default CBFS
header (as it ought to) when multiple CBFS images support is enabled.

BRANCH=storm
BUG=chrome-os-partner:34161, chromium:445938
TEST=with the rest of the patches applied storm boots all the way inot
     the Linux prompt

Change-Id: I5e029d95c5cb085794c7bf5f44513b2144661e38
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 75b2c2ef6c8287db7c3e5879cacfd5dcba4391ac
Original-Change-Id: I5c352921b4c9b6a3294f4658d174e0842d2ee365
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/237661
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9770
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/arch/arm/armv7/bootblock_simple.c

@@ -46,6 +46,8 @@ void main(void)
 	exception_init();
 #endif
 
+	cbfs_set_header_offset(0);
+
 	bootblock_soc_init();
 	bootblock_mainboard_init();