vboot: Exclude platform specific files from RW cbfs

Add a Kconfig option to allow platforms to exclude specific files
from being copied from RO into RW sections.

BUG=b:65484600
TEST=Exclude apu/amdfw from the RW cbfs sections

Change-Id: I7723b63392c1620b75ceb6d8e25fe1ce2c75cf18
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/21899
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
2 files changed