chromeos: Unconditionally clear the EC recovery request

Add the empty weak function clear_recovery_mode_switch().

Problem:
If GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC is set,
the following will happen:

1. Boot device in recovery mode with Esc + F3 + Pwr.
2. Turn device off with Pwr button.
3. Turn device on with Pwr button.

Device still boots to recovery screen with
recovery_reason:0x02 recovery button pressed.

If GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC isn't set, turning the
device off and on again  with the Pwr button does a normal boot.

Solution:
Unconditionally clear the recovery flag.

BUG=chromium:279607
BRANCH=TOT
TEST=Compile OK.

Original-Change-Id: Ie1e3251a6db12e75e385220e9d3791078393b1bf
Original-Signed-off-by: Sheng-Liang Song <ssl@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/197780
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-by: Randall Spangler <rspangler@chromium.org>
Original-Commit-Queue: Sheng-liang Song <ssl@google.com>
Original-Tested-by: Sheng-liang Song <ssl@google.com>
(cherry picked from commit 18908bb64cef34ca41812814817ef887961bed34)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: I71ca9f3ea8d816c865375ec66a0603ca211f23ae
Reviewed-on: http://review.coreboot.org/7895
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins)