drm/amdgpu: add prototype for ip dump

Add the prototype to dump ip registers
for all ips of different asics and set
them to NULL for now. Based on the
requirement add a function pointer for
each of them.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>