Add lvm/svm intrinsic instructions and a regression test. Change
RegisterInfo to specify that VM0/VMP0 are constant and reserved
registers. This modifies a vst regression test, so update it.
Also add pseudo instructions for VM512 register classes
and mechanism to expand them after register allocation.
Reviewed By: simoll
Differential Revision: https://reviews.llvm.org/D91541
Kazushi (Jam) Marukawa