media: mtk-vcodec: Refactor vcodec pm interface

Using the needed params for pm init/release function and remove unused
param mtkdev in 'struct mtk_vcodec_pm'.

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Reviewed-by: Tzung-Bi Shih <tzungbi@google.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Steve Cho <stevecho@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>