media: hantro: Add helpers to prepare/finish a run

And use them where appropriate.

We might want to move hantro_{prepare,finish}_run() calls to
device_run() and have a 2-step approach similar to cedrus (prepare +
trigger) at some point, but let's keep that for later.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>