drm/amdkfd: remove obsolete codes for kfd_mmap

drm/amdkfd: remove obsolete codes for kfd_mmap

kfd_reserved_mem_mmap is only for mapping CWSR on APU in IOMMUv2
mode, which is no longer supported, and qpd->cwsr_base has been
set before calling kfd_process_init_cwsr_apu, which is the only
caller for KFD_MMAP_TYPE_RESERVED_MEM, so kfd_process_init_cwsr_apu
is not functional anymore, remove them together. On the other hand,
it will fix a vulnerability issue to abuse KFD_MMAP_TYPE_RESERVED_MEM
of kfd_mmap from userspace.

Signed-off-by: Eric Huang <jinhuieric.huang@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>