media: hevc: Remove RPS named flags

Marking a picture as long-term reference is valid for DPB but not for RPS.
Change flag name to match with the description in HEVC spec chapter
"8.3.2 Decoding process for reference picture set".

PocStCurrBefore, PocStCurrAfter, PocLtCurr lists could be built by the
kernel from the DPB entries struct v4l2_hevc_dpb_entry, using the
information in the rps field. This way RPS flags becomes useless and are
removed.

This patch breaks the staging HEVC API because it introduces a new flag,
changes a field name in v4l2_hevc_dpb_entry structure and removes
V4L2_HEVC_DPB_ENTRY_RPS_* flags.

[hverkuil: fixed some typos]

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>