media: venus: vdec: Handle DRC after drain

If the DRC is near the end of the stream the client
may send a V4L2_DEC_CMD_STOP before the DRC occurs.
V4L2_DEC_CMD_STOP puts the driver into the
VENUS_DEC_STATE_DRAIN state.  DRC must be aware so
that after the DRC event the state can be restored
correctly.

Signed-off-by: Fritz Koenig <frkoenig@chromium.org>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>