Keyborg: improve panel discharge
Keyborg: improve panel discharge

This fix includes:
  - A faster discharge procedure
  - Added discharge steps between scanning two columns. This is to
    prevent the shadow "wraps around" to the beginning of the next
    column, which is much harder to filter out.

BUG=None
TEST=Press hard on the end of one column. Check the shadow doesn't wrap
around to the next column.
BRANCH=None

Change-Id: Ie1342f7778d0fe18a0ec2086af79d5e459f1cd7d
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/202073
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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