On media drivers, debugging messages should be grouped into
categories, as this makes easier to debug the driver.

In the case of saa7134, the core has 2 debug categories, one
for IRQ, and another one for the core itself. The IRQ have
actually 2 levels of debug.

So, instead of using pr_dbg(), where everything would be in
the same box, let's define two macros that use pr_fmt(),
one for the core, and another one for irq.

With that, we can replace the remaining printk() occurrences
at the core to use either core_dbg() or irq_dbg(), depending
on the group of debug macros that need to be enabled.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>