Twinkie: Enable flashing with dfu-util.
Twinkie: Enable flashing with dfu-util.

Twinkie only has test points for uart connection so nominally it will
need to be programmed via DFU mode over USB micro-B connection.

This CL changes from programming via flash_stm32 function and instead
adds dfu support.

BUG=chrome-os-partner:28337
TEST=util/flash_ec --board=twinkie successfully programs twinkie f/w

Change-Id: Ia5433b569579bb879bd405e98921450764510a73
Reviewed-on: https://chromium-review.googlesource.com/204749
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Commit-Queue: Todd Broch <035f5b1f817cbb94019cec357b99778115602b63@chromium.org>
Tested-by: Todd Broch <035f5b1f817cbb94019cec357b99778115602b63@chromium.org>

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