media: staging: rkisp1: change fields names from fmt_type to pixel_enc

The fields 'fmt_type' in the structs
'rkisp1_rsz_config', 'rkisp1_isp_mbus_info' are of type
'v4l2_pixel_encoding' so it is nicer to change their name to
'pixel_enc'. Also change the define 'RKISP1_DEF_FMT_TYPE' to
'RKISP1_DEF_PIXEL_ENC'

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>