media: vicodec: rename and use proper fwht prefix for codec

The codec source is generic and not vicodec specific. It can be used
by other drivers or userspace as well. So rename the source and header
to something more generic (codec-fwht.c/h) and prefix the defines, types
and functions with fwht_.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>