x86: i8254.c: Add pr_fmt(fmt)

- Add pr_fmt(fmt) "pit: " fmt
 - Strip pit: prefixes from pr_debug

Signed-off-by: Joe Perches <joe@perches.com>
LKML-Reference: <bbd4de532f18bb7c11f64ba20d224c08291cb126.1260383912.git.joe@perches.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>