[X86] Add more load folding patterns for blend instructions as a follow up to r354363.

This avoids depending on the peephole pass to do load folding.

Also adds some load folding for some insert_subvector patterns that use blend.

All of this was found by temporarily adding TB_NO_FORWARD to the blend immediate entries in the load folding tables.

I've added -disable-peephole to some of the affected tests from that experiment to ensure we're testing isel patterns.

llvm-svn: 354511