This adds new intrisics to support the LDAP1 and STL1 Advanced SIMD
(Neon) instructions introduced as part of FEAT_LRCPC3.
The new intrinsics vldap1(q)_lane/vstl1(q)_lane generate IR code
similar to the existing vld1(q)_lane/st1(q)_lane ones, but capturing
the difference in the atomic release/acquire memory model.
The LLVM code generation changes to ensure that this instruction pair
is lowered to the correct LDAP1/STL1 instructions will be covered in a
separate commit.
Based on a patch by Sam Elliott.