arm64: Set LOG_LEVEL=0 for BL31 if coreboot does not use serial

Even if DEBUG=0, BL31 puts NOTICE(..) messages on serial console. Set
LOG_LEVEL=0 if coreboot does not use serial.

BUG=None
BRANCH=None
TEST=Compiles successfully and no console output from bl31 for
production images.

Change-Id: Ie77bcac3e2a0d314545b6811327c413536c77fb9
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: e8e3bcbf6249c80850a87dd66f34d3ff36158641
Original-Change-Id: I1415a3816cd2fa9dd05bcbd36ac0abc3f2759960
Original-Signed-off-by: Furquan Shaikh <furquan@google.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/286150
Original-Tested-by: Furquan Shaikh <furquan@chromium.org>
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Original-Commit-Queue: Furquan Shaikh <furquan@chromium.org>
Original-Trybot-Ready: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: http://review.coreboot.org/11014
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins)
1 file changed