Add and use #define pr_fmt/dev_fmt, and remove #define PFX

This also prefixes some messages that were not previously prefixed.

Miscellanea:

o Convert printk(KERN_<level> to pr_<level>(
o Use %s, __func__ where appropriate
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>