gpu: drm: amd/radeon: Convert printk(KERN_<LEVEL> to pr_<level>

Use a more common logging style.

Miscellanea:

o Coalesce formats and realign arguments
o Neaten a few macros now using pr_<level>

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>