media: rockchip/vpu: Move encoder logic to a common place

The V4L2/VB2 implementation for the encoder and decoder logic are very
similar, so let's rename rockchip_vpu_enc.c file into
rockchip_vpu_v4l2.c and remove the _enc_ part in objects/functions
exposed in rockchip_vpu_v4l2.h. We also rename the enc_queue_init()
function (in rockchip_vpu_drv.c) queue_init() since it will be used
to initialize both type of queues.

The implementation itself will be patched to support the decoding case
when decoder support is added.

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