vboot_reference: set CC=armv7a-cros-linux-gnueabihf-gcc for ARM
vboot_reference: set CC=armv7a-cros-linux-gnueabihf-gcc for ARM

We want to drop armv7a-cros-linux-gnueabi toolchain, so we need
to use armv7a-cros-linux-gnueabihf-gcc instead.

BRANCH=None
BUG=chromium:711369
TEST=emerge-kevin vboot_reference

Change-Id: Ie6831079162916eb11e98da3aecdcd8c0bd0d82d
Reviewed-on: https://chromium-review.googlesource.com/1241856
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Tested-by: Yunlian Jiang <8ca9e07d8da722742b3f5a8340e0afab8cf1248e@chromium.org>
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot