Plankton: Support DFU mode
Plankton: Support DFU mode

This includes:
  - Enabling SBU path for debug USB usage in USB mode (not in DP mode)
  - Add a console command to enable DFU mode for lab devices. This
    requires the additional Silego chip on the device.

BRANCH=None
BUG=None
TEST=Hook up a Ryu with the additional Silego chip. Issue 'dfu' command
and see DFU device in 'lsusb' output. Issue the command again and the
device goes away.

Change-Id: I3f942c6abe52784351f2242c9b0b6400e9b2b6fd
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@google.com>
Reviewed-on: https://chromium-review.googlesource.com/247350
Tested-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Commit-Queue: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>

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