detachables: Set fw screen timeout to 30 secs upon button press

For detachables, the short delay is to fast to them to read/choose
options.  Setting timeout to 30 seconds once user starts scrolling
through the menu.  If no action is taken by the user, will retain
the short delay timeout.

BUG=b:63056097, b:35585623
BRANCH=None
TEST=reboot with gbb flag bit 1 enabled and ensure using short delay.
     reboot and press volume button and make sure using long delay.
     reboot and make sure short delay performed again upon reboot.
     reboot and make sure gbb flag bit 1 = 0 and make sure long delay
     still working as expected.

Change-Id: I31e3ca8aff6b29abca70ca9587deae7f6443d837
Signed-off-by: Shelley Chen <shchen@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/563817
Reviewed-by: Randall Spangler <rspangler@chromium.org>
3 files changed