media: uapi: mpeg2: Cleanup flags

Our current MPEG-2 uAPI uses 1-byte fields for MPEG-2
boolean syntax elements. Clean these by adding a 'flags'
field and flag macro for each boolean syntax element.

A follow-up change will refactor this uAPI so we don't need
to add padding fields just yet.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Tested-by: Jonas Karlman <jonas@kwiboo.se>
Tested-by: Jernej Skrabec <jernej.skrabec@siol.net>
Reviewed-by: Jernej Skrabec <jernej.skrabec@siol.net>
Tested-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>