drm/amd: Add new kfd-->kgd interface for gart usage

This patch adds two new functions to the kfd-->kgd interface:

init_gtt_mem_allocation, which allocate a large enough buffer on the amdkfd
needs, such as mqds, hpds, kernel queue, fence and runlists. This function
is only called once per GPU device. The size of the allocated buffer is
based on the maximum number of HSA processes and maximum number of queues
per HSA process (two amdkfd kernel module parameters).

free_gtt_mem, which frees a buffer that was allocated on the gart aperture.

Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Reviewed-by: Alexey Skidanov <Alexey.skidanov@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>