grunt: Add cr50 UART

BUG=None.
TEST=Verify cr50 UART is functional w/ servo_v2.
BRANCH=None.

Change-Id: I52239cb1fe285e6be98606bd7408fdb1ba3ab1b5
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/868500
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Shawn N <shawnn@chromium.org>
Reviewed-by: Edward Hill <ecgh@chromium.org>
Reviewed-by: Chris Ching <chingcodes@chromium.org>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
2 files changed