CHROMIUM: config: reven: Enable DRM_FBDEV_EMULATION

This option adds support for legacy fbdev emulation which is required on
older radeon devices to prevent strobing during boot before the splash
screen.

After normalizing the configs using `./chromeos/scripts/kernelconfig
olddefconfig` the config is not set directly but is enabled by
default.

Signed-off-by: Allen Ballway <ballway@chromium.org>

BUG=b:350055657
TEST=`./chromeos/scripts/kernelconfig olddefconfig` shows no changes
TEST=Boot device requiring fbdev emulation (e.g. HP Probook 655)
TEST=Confirm display does not strobe while booting.

Change-Id: Ie2139b63f56b1cb80b8cdcb40b5328cd7bcd61ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/5888353


Tested-by: Allen Ballway <ballway@google.com>
Reviewed-by: Jeffery Miller <jefferymiller@google.com>
Commit-Queue: Allen Ballway <ballway@google.com>
Signed-off-by: Mateusz Urbańczyk <urbanczyk@google.com>