drm/radeon: add si tile mode array query v3

Allow userspace to query for the tile mode array so userspace can properly
compute surface pitch and alignment requirement depending on tiling.

v2: Make strict aliasing safer by casting to char when copying
v3: merge fix from Christian

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>