mb/google/volteer: Reorganize FMAP

mb/google/volteer: Reorganize FMAP

This change reorganizes FMAP for volteer to make use of the lower
16MiB of the SPI flash for RW_SECTION_A and RW_MISC in addition to
RW_LEGACY. This is now possible because TGL supports memory mapping of
BIOS region greater than 16MiB.

Following changes are made in chromeos.fmd as part of this:
1. Move RW_SECTION_A and RW_MISC to lower 16MiB.
2. Reduce size of RW_LEGACY to 2MiB since we longer need to use it as
a placeholder in the lower half of the SPI flash.
3. Reduce size of RW_ELOG to 4KiB as coreboot does not support a
larger region for ELOG.
4. Increase WP_RO to 8MiB to allow larger space for firmware
screens. GBB size is thus increased to 448KiB.

BUG=b:171534504

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: I0c3c0af94183a80c23d196422d3c8cf960b9d9f5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48187
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>