drm/amdgpu/trace: Add tracepoints to MMIO read/writes

Add tracepoints to the MMIO read/write so we can log
MMIO traffic.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>