drm/amdgpu: fix no full coverage issue for gprs initialization

The wave's number per simd in aldebaran is changed to 8, so it is
impossible to use old algorithm to initiate all sgprs with one
threadgroup. The new algorithm firstly use three threadgroups to
initiate most sgprs simultaneously and then use another threadgroup with
4 waves to cover other uninitiated sgprs.

v2:
Add more description about the new algorithm to clear sgprs and add some
comment for shader binaries

Signed-off-by: Dennis Li <Dennis.Li@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>