Convert STK_<LEVEL> to pr_<level> to use the typical kernel logging.
Add a define for pr_fmt.  No change in logging output.

Miscellanea:

o Remove now unused PREFIX and STK_<LEVEL> macros
o Realign arguments
o Use pr_<level>_ratelimited
o Add a few missing newlines to formats
Signed-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NHans Verkuil <hansverk@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>