[AArch64] Replace sme-i64 by sme-i16i64 and sme-f64 by sme-f64f64

The names in developer.arm for these SME features are:
  HaveSMEI16I64 and HaveSMEF64F64
so the new flag names are consistent with the documentation page

Reviewed By: sdesmalen, c-rhodes

Differential Revision: https://reviews.llvm.org/D135974