drm/amdkfd: Retrieve SDMA numbers from amdgpu

Instead of hard coding the number of sdma engines and the number of
sdma_xgmi engines in the device_info table, get the number of toal SDMA
instances from amdgpu. The first two engines are sdma engines and the
rest are sdma-xgmi engines unless the ASIC doesn't support XGMI.

v2: add kfd_ prefix to non static function names

Signed-off-by: Amber Lin <Amber.Lin@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>