ff_get_packet_palette() and ff_reshuffle_raw_rgb() belong together:
E.g. the former takes the return value of the latter as argument.
So move ff_get_packet_palette() to rawutils.c (which consists solely
of ff_reshuffle_raw_rgb()).
Also add a separate header for these two functions.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
