media: mediatek: vcodec: add remove function for decoder platform driver

Need to disable decoder power when remove decoder hardware driver, adding
remove callback function in the definition of platform driver.

Fixes: c05bada3 ("media: mtk-vcodec: Add to support multi hardware decode")
Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>