R600: Remove predicated_break inst

We were using two instructions for similar purpose : break and
predicated break. Only predicated_break was emitted and it was
lowered at R600ControlFlowFinalizer to JUMP;CF_BREAK;POP.
This commit simplify the situation by making AMDILCFGStructurizer
emit IF_PREDICATE;BREAK;ENDIF; instead of predicated_break (which
is now removed).

There is no functionality change.
TableGen: Enumerate Schedule Model too.
R600: Use SchedModel enum for is{Trans,Vector}Only functions
R600: Don't mix LDS and non-LDS instructions in the same group

There are a lot of restrictions on instruction groups that contain
LDS instructions, so for now we will be conservative and not packetize
anything else with them.
R600: Non vector only instruction can be scheduled on trans unit
R600: Avoid more than 4 literals in the same instruction group at scheduling
R600: Do not mergevector after a vector reg is used

If we merge vector when a vector is used, it will generate an artificial
antidependency that can prevent 2 tex/vtx instructions to use the same
clause and thus generate extra clauses that reduce performance.

There is no test case as such situation is really hard to predict.