bmpblk: reduce volteer screen colors

Reduce screen colors from 5 to 4 to reduce image size on the
firmware screens because Volteer is out of SPI flash space and
the build is failing.

BUG=b:170305053
BRANCH=none
TEST="emerge-volteer bmpblk coreboot chromeos-bootimage" and verify
the build succeeds.

Change-Id: Ibda123281d711f16712eda3904e1c7d399fb1155
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/bmpblk/+/2460988
Tested-by: Nick Vaccaro <[email protected]>
Reviewed-by: Dossym Nurmukhanov <[email protected]>
Reviewed-by: Tim Wawrzynczak <[email protected]>
Reviewed-by: Shelley Chen <[email protected]>
Commit-Queue: Nick Vaccaro <[email protected]>
1 file changed