[AArch64] Fix return type of Neon scalar comparison intrinsics

The following should have unsigned return types
but were signed:
vceqd_s64 vceqzd_s64 vcged_s64 vcgezd_s64
vcgtd_s64 vcgtzd_s64 vcled_s64 vclezd_s64
vcltd_s64 vcltzd_s64 vtstd_s64

See https://developer.arm.com/documentation/ihi0073/latest

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D88009