[GlobalISel][AArch64] Allow CallLowering to handle types which are normally

[GlobalISel][AArch64] Allow CallLowering to handle types which are normally
required to be passed as different register types. E.g. <2 x i16> may need to
be passed as a larger <2 x i32> type, so formal arg lowering needs to be able
truncate it back. Likewise, when dealing with returns of these types, they need
to be widened in the appropriate way back.

Differential Revision: https://reviews.llvm.org/D60425

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358032 91177308-0d34-0410-b5e6-96231b3b80d8