arm64: Pass COREBOOT flag to ARM TF, always enable logging

arm64: Pass COREBOOT flag to ARM TF, always enable logging

This patch changes the way coreboot builds ARM TF to pass the new
COREBOOT flag introduced with the following pull request:

  https://github.com/ARM-software/arm-trusted-firmware/pull/1193

Since the new coreboot support code supports the CBMEM console, we need
to always enable LOG_LEVEL INFO. Supporting platforms will parse the
coreboot table to conditionally enable the serial console only if it was
enabled in coreboot as well.

Also remove explicit cache flushes of some BL31 parameters. Turns out we
never really needed these because we already flush the whole cache when
disabling the MMU, and we were already not doing it for most parameters.

Change-Id: I3c52a536dc6067da1378b3f15c4a4d6cf0be7ce7
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/23558
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>