vboot_reference: Provide crossystem interface stubs for mips
vboot_reference: Provide crossystem interface stubs for mips

BUG=chromium:358418
TEST=emerge-mipsel-o32-generic vboot_reference now builds.
BRANCH=none

Change-Id: Ia1414dfdef00c5b22ed0971fad814ef761b32b86
Reviewed-on: https://chromium-review.googlesource.com/193050
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Tested-by: Gaurav Shah <2987db6a10bcfe664554a372d01e80df7fd325a3@chromium.org>
Commit-Queue: Gaurav Shah <2987db6a10bcfe664554a372d01e80df7fd325a3@chromium.org>

acorn-marvell/vboot_reference,ccaapton/vboot_reference,ccaapton/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,ccaapton/vboot_reference,ccaapton/vboot_reference,coreboot/vboot,geekboxzone/mmallow_external_vboot_reference,acorn-marvell/vboot_reference,coreboot/vboot,coreboot/vboot