[SelectionDAG][ARM][AArch64][Hexagon][RISCV][X86] Add SDNPCommutative to fma...

[SelectionDAG][ARM][AArch64][Hexagon][RISCV][X86] Add SDNPCommutative to fma and fmad nodes in tablegen. Remove explicit commuted patterns from targets.

X86 was already specially marking fma as commutable which allowed
tablegen to autogenerate commuted patterns. This moves it to the target
independent definition and fix up the targets to remove now
unneeded patterns.

Unfortunately, the tests change because the commuted version of
the patterns are generating operands in a different than the
explicit patterns.

Differential Revision: https://reviews.llvm.org/D91842