media: rkvdec: Drop unneeded per_request driver-specific control flag

Currently, the drivers makes no distinction between per_request
and mandatory, as both are used in the same request validate check.

The driver only cares to know if a given control is
required to be part of a request, so only one flag is needed.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Tested-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>