[Aarch64] Add v8.2-a half precision element extract intrinsics

Summary:
Implements the intrinsics define on the ACLE to extract half precision fp scalar elements from float16x4_t and float16x8_t vector types.
a.k.a:
vduph_lane_f16
vduph_laneq_f16

Reviewers: pablooliveira, olista01, LukeGeeson, DavidSpickett

Reviewed By: DavidSpickett

Subscribers: DavidSpickett, javed.absar, kristof.beyls, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D60272

llvm-svn: 358276