drm/ttm: Bump TTM_NUM_MEM_TYPES to 9 (Prep for AMDGPU_PL_MMIO_REMAP)

Increase TTM_NUM_MEM_TYPES from 8 to 9 to accommodate the upcoming
AMDGPU_PL_MMIO_REMAP placement.

Cc: Alex Deucher <alexander.deucher@amd.com>
Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>