R600/SI: remove nonsense select pattern

Fortunately this pattern never matched, otherwise
we would have generated incorrect code.

Signed-off-by: Christian K??nig <christian.koenig@amd.com>
R600: Use new tablegen syntax for patterns

All but two patterns have been converted to the new syntax.  The
remaining two patterns will require COPY_TO_REGCLASS instructions, which
the VLIW DAG Scheduler cannot handle.