[media] saa7134: better handle core debug messages

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>