[X86] Add InstFixup for masked `unpck{l|h}pd` -> masked `shufpd`

[X86] Add InstFixup for masked `unpck{l|h}pd` -> masked `shufpd`

This is a follow up D147507 which removed the prior transformation to
`shufps` which was incorrect as the mask was for 64-bit double
elements, not 32-bit float elements. Using `shufpd` for the
replacement, however, preserves the mask semantics and has the same
benefits as `shufps`.

Reviewed By: pengfei, RKSimon

Differential Revision: https://reviews.llvm.org/D147541