Patch merged into coreboot/master: ti/beaglebone: Define arch for omap-header build

the following patch was just integrated into master:
commit 555c9f9252c40f54ce74f7b01d8e40825dbd7bda
Author: Kyösti Mälkki 
Date:   Wed Dec 7 15:01:54 2016 +0200

ti/beaglebone: Define arch for omap-header build

Required to add rules.h as default include, otherwise we get error:

./src/include/rules.h:128:5: error:
          "__COREBOOT_ARM_ARCH__" is not defined [-Werror=undef]

Previously, rules.h was not included in omap-header build at all.

Change-Id: I75265916856f2f21f7966619ea65d63acd599e2f
    Signed-off-by: Kyösti Mälkki 
    Reviewed-on: https://review.coreboot.org/17746
    Tested-by: build bot (Jenkins)
    Reviewed-by: Aaron Durbin

See https://review.coreboot.org/17746 for details.

-gerrit