media: mtk-vcodec: Remove mtk_vcodec_release_enc_pm

There are only two lines in mtk_vcodec_release_enc_pm, using
pm_runtime_disable and put_device instead directly.

Move pm_runtime_enable outside mtk_vcodec_release_enc_pm to symmetry with
pm_runtime_disable, after that, rename mtk_vcodec_init_enc_pm to *_clk
since it only has clock operations now.

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>