drm/radeon: Remove now unused functions in radeon driver

With the dropped inlines gccs starts warning about genuinely unused
functions. Remove r600_bpe_from_format, evergreen_cs_track_validate_cb,
evergreen-cs_packet_next_is_pkt3_nop which are all unused.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>