Acknowledge Ctrl+U faster
Acknowledge Ctrl+U faster

When the user hits Ctrl+U on the dev screen, we used to change the
screen only after we enumerate the USB devices, load the kernel from USB
mass storage and boot it (about 4 seconds on the current firmware).
Let's blank the screen earlier to show we got the key press.

BUG=chrome-os-partner:7563
TEST=on a Stumpy in developer, hit Ctrl+U on the dev screen with an
invalid key, then a valid key. Check which screen are displayed and how
long it takes to get a new display after the key strokes.

Change-Id: Ifc73b56055bcd50360d71c1cb6dee052d0fdf9aa
Reviewed-on: https://gerrit.chromium.org/gerrit/14395
Reviewed-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Commit-Ready: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Tested-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

geekboxzone/mmallow_external_vboot_reference,ionave/seismograph,coreboot/vboot,acorn-marvell/vboot_reference,ccaapton/vboot_reference,ccaapton/vboot_reference,acorn-marvell/vboot_reference,geekboxzone/mmallow_external_vboot_reference,geekboxzone/mmallow_external_vboot_reference,coreboot/vboot,ccaapton/vboot_reference,ionave/seismograph,coreboot/vboot,marineam/seismograph,geekboxzone/mmallow_external_vboot_reference,geekboxzone/mmallow_external_vboot_reference,ionave/seismograph,acorn-marvell/vboot_reference,marineam/seismograph,ccaapton/vboot_reference,coreboot/vboot,marineam/seismograph,marineam/seismograph,acorn-marvell/vboot_reference,coreboot/vboot