depthcharge/ui: Drop support of VB2_SCREEN_BLANK

Stop supporting screen drawing for VB2_SCREEN_BLANK. Always enable
backlight in init_screen().

BUG=none
TEST=emerge-asurada depthcharge
BRANCH=none

Cq-Depend: chromium:2793448
Change-Id: I112facd4e09a24cae31094fae89c385ca38a0518
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/depthcharge/+/2793450
Reviewed-by: Julius Werner <jwerner@chromium.org>
2 files changed