[AArch64] Fixed vget/vset_lane_f16 implementation

Replaced cast and vreinterepret operations with
code to reinterpret bitwise the types float16_t and
int16_t.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201112 91177308-0d34-0410-b5e6-96231b3b80d8