drm/amdkfd: report xgmi bandwidth between direct peers to the kfd

Report the min/max bandwidth in megabytes to the kfd for direct
xgmi connections only.  Indirect peers will report 0 since
indirect route is unknown.

Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>