[TableGen] Add generation of argument register lists

There are cases, like with -fzero-call-used-regs,  where we need to know
which registers can be used by a certain calling convention. This change
generates a list of registers used by each calling convention defined in
*CallingConv.td.

Calling conventions that use registers conditioned on Swift have those
registers placed in a separate list. This allows us to be flexible about
whether to use the Swift registers or not.

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D125421