drm/amdgpu: map doorbell for the requested userq

drm/amdgpu: map doorbell for the requested userq

Introduce db_info structure to the populate the doorbell
information that is required to be mapped.

Made changes to the doorbell mapping func more generic,
by taking parameters that vary based on IPs and/or usecase
into db_info structure.

v2 - Fix space alignment and checkpatch warnings(Shashank)

Signed-off-by: Saleemkhan Jamadar <saleemkhan.jamadar@amd.com>
Reviewed-by: Shashank Sharma <shashank.sharma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>