drm/amdgpu: Prefer dev_* variant over printk in amdgpu_atpx_handler.c

Changed from printk to dev_* variants so that
we get better debug info when there are multiple GPUs
in the system.

Fixes other style issue:

ERROR: open brace '{' following function definitions go on the next line
WARNING: printk() should include KERN_<LEVEL> facility level

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>