ectool: Add enter_gfu to support PD flashing.
ectool: Add enter_gfu to support PD flashing.

Flashing PD devices works through ectool but only when device has
already entered GFU alternate mode.  This CL adds ability to force
that entry for devices with default policy engine does not already do
that.

Signed-off-by: Todd Broch <035f5b1f817cbb94019cec357b99778115602b63@chromium.org>

BRANCH=samus
BUG=chrome-os-partner:33947
TEST=manual,

1. On hoho flash RW successfully
  ectool --name cros_pd flashpd 4 1 hoho.ec.RW.bin

Change-Id: Idd320cf91644f0c1bff87767ab20049d86aa86c6
Reviewed-on: https://chromium-review.googlesource.com/236959
Reviewed-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Tested-by: Todd Broch <035f5b1f817cbb94019cec357b99778115602b63@chromium.org>

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