ath: Add and use ath_printk and ath_<level>

Add ath_printk and ath_<level> similar to
dev_printk and dev_<level> from device.h

This allows a more gradual rename of ath_print
to to ath_dbg or perhaps ath_debug.

This basically removes debug.h leaving
only an #define ath_printk ath_dbg
there and moving all the ATH_DBG_<foo>
enums to ath.h

I do not think there's much purpose for struct
ath_common * being passed to the ath_printk
functions, but perhaps there might be.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>