build_image: Add support for building mips

Provide mips arch definitions wherever needed. For now,
all arch specific cases are handled the same as arm.

BUG=chromium:365867
TEST=build_image --board=mipsel-o32-generic base
CQ-DEPEND=CL:201010

Change-Id: I462ef38c05c9d6f440e8ec1331c995f69f781fe8
Reviewed-on: https://chromium-review.googlesource.com/199995
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Gaurav Shah <gauravsh@chromium.org>
Commit-Queue: Gaurav Shah <gauravsh@chromium.org>
4 files changed