[ARM,MVE] Add ACLE intrinsics for VCVT[ANPM] family.
These instructions convert a vector of floats to a vector of integers
of the same size, with assorted non-default rounding modes.
Implemented in IR as target-specific intrinsics, because as far as I
can see there are no matches for that functionality in the standard IR
Reviewers: MarkMurrayARM, dmgreen, miyuki, ostannard
Reviewed By: dmgreen
Subscribers: kristof.beyls, hiraditya, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D75255