media: uapi: h264: Rename and clarify PPS_FLAG_SCALING_MATRIX_PRESENT

Applications are expected to fill V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX
if a non-flat scaling matrix applies to the picture. This is the case if
SPS scaling_matrix_present_flag or PPS pic_scaling_matrix_present_flag
are set, and should be handled by applications.

On one hand, the PPS bitstream syntax element signals the presence of a
Picture scaling matrix modifying the Sequence (SPS) scaling matrix.
On the other hand, our flag should indicate if the scaling matrix
V4L2 control is applicable to this request.

Rename the flag from PPS_FLAG_PIC_SCALING_MATRIX_PRESENT to
PPS_FLAG_SCALING_MATRIX_PRESENT, to avoid mixing this flag with
bitstream syntax element pic_scaling_matrix_present_flag,
and clarify the meaning of our flag.

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>