ryu: properly enable UART Rx DMA for P2 boards
ryu: properly enable UART Rx DMA for P2 boards

We defined the DMA channel for UART Rx DMA to use, but we didn't
actually enable it.

BRANCH=None
BUG=chrome-os-partner:32660
TEST=Check the console is still responsive

Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/225280
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit e1a6096dbe6cbdd21bc5d1a9ee6759b516ddbc73)
Signed-off-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>

Change-Id: I0dcbeeccb3a4213305c84ec5238e6e9dbee09b33
Reviewed-on: https://chromium-review.googlesource.com/225750
Tested-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>
Reviewed-by: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>
Commit-Queue: Duncan Laurie <70662b43bc1a20b57ded72a2b08be88dd0da4841@chromium.org>

thehobn/ec,thehobn/ec,thehobn/ec,thehobn/ec