aarch64: Add aarch64-elf toolchain to crossgcc Makefile

BUG=None
BRANCH=none
TEST=Build crosgcc for aarch64-elf
Signed-off-by: Marcelo Povoa <marcelogp@chromium.org>

Original-Change-Id: Ifc886b6bd125552855ad1cf49ee7c1b7a0350895
Original-Reviewed-on: https://chromium-review.googlesource.com/186413
Original-Reviewed-by: Stefan Reinauer <reinauer@chromium.org>
Original-Tested-by: Marcelo Póvoa <marcelogp@chromium.org>
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
Original-Commit-Queue: Marcelo Póvoa <marcelogp@chromium.org>
(cherry picked from commit 9959047c82c96108f4bdedad1db0219fcdc85378)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: I5e781443bb11a7db3420bb8cfc447de8494b1d24
Reviewed-on: http://review.coreboot.org/7661
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Tested-by: build bot (Jenkins)
1 file changed