keyboard: Preserve keystroke enable state.
keyboard: Preserve keystroke enable state.

Preserve the state of keystroke_enabled to prevent keystrokes from being
initially disabled on RO --> RW transition. This will allow us to use
the keyboard on EC cold boot.

BUG=chrome-os-partner:20430.
TEST=Manual. Verify keyboard works on EC cold boot on Peppy.
BRANCH=None.

Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Change-Id: I603a73ee0f8435c91d430a64803add345c92f025
Reviewed-on: https://gerrit.chromium.org/gerrit/59798
Reviewed-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>

alterapraxisptyltd/chromium-ec,longsleep/ec,mtk09422/chromiumos-platform-ec,alterapraxisptyltd/chromium-ec,coreboot/chrome-ec,md5555/ec,mtk09422/chromiumos-platform-ec,fourier49/BIZ_EC,longsleep/ec,coreboot/chrome-ec,coreboot/chrome-ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,alterapraxisptyltd/chromium-ec,mtk09422/chromiumos-platform-ec,fourier49/BIZ_EC,md5555/ec,eatbyte/chromium-ec,fourier49/BZ_DEV_EC,thehobn/ec,fourier49/BIZ_EC,gelraen/cros-ec,mtk09422/chromiumos-platform-ec,thehobn/ec,coreboot/chrome-ec,gelraen/cros-ec,longsleep/ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,alterapraxisptyltd/chromium-ec,longsleep/ec,thehobn/ec,fourier49/BZ_DEV_EC,md5555/ec,fourier49/BZ_DEV_EC,gelraen/cros-ec,eatbyte/chromium-ec,eatbyte/chromium-ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,gelraen/cros-ec,akappy7/ChromeOS_EC_LED_Diagnostics,md5555/ec,fourier49/BIZ_EC,coreboot/chrome-ec,thehobn/ec