AMDGPU: Remove incorrect uses of SubtaretPredicate around DS_Reals (#85001)

SubtargetPredicate is copied from DS_Pseudo to DS_Real. We should not
use another SubtargetPredicate assignment around DS_Real, because doing
so will override the predicate from DS_Pseudo.

For example, for DS_ADD_RTN_F64, SubtargetPredicate was set to
HasLdsAtomicAddF64 in Pseudo. And it will be overridden to isGFX90APlus
if we assign isGFX90APlus to SubtargetPredicate in Real definition.