drm/radeon: Initialize compute vmid

This patch moves to radeon the initialization of compute vmid.

That initializations was done in kfd-->kgd interface, but doing it in radeon
as part of radeon's H/W initialization routines is more appropriate.

In addition, this simplifies the kfd-->kgd interface.

The patch removes the function from the interface file and from the interface
declaration file.

The function initializes memory apertures to fixed base/limit address and non
cached memory types.

Signed-off-by: Ben Goz <ben.goz@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>