flash_ec: Add support for kitty
flash_ec: Add support for kitty

Make board kitty to use flash_stm32.

BUG=chrome-os-partner:33035
BRANCH=None
TEST=Run util/flash_ec on kitty, verify flashing
complete successfully.

Change-Id: I302cfc85bfe5fa36fdf1a61d59b4dc21b36cc06a
Signed-off-by: Ken Chang <0d90554bf9cc6dfe3790debef13719c5538556c7@nvidia.com>
Reviewed-on: https://chromium-review.googlesource.com/224231
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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