[Hexagon] Add support for proper handling of H and L constraints

H -> High part of reg pair.
L -> Low part of reg pair.

Patch by Sundeep Kushwaha.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276773 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed