drm/amdkfd: Eliminate unnecessary kernel queue function pointers

Up to this point, those functions are all the same for all ASICs, so
no need to call them by functions pointers. Removing the function
pointers will greatly increase the code readablity. If there is ever
need for those function pointers, we can add it back then.

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