aarch64: Rename FLAG_NONE to FLAG_DEFAULT

aarch64: Rename FLAG_NONE to FLAG_DEFAULT

This patch renames to FLAG_NONE to FLAG_DEFAULT.  "NONE" suggests
that the function has no side-effects, whereas it actually means
that floating-point operations are assumed to read FPCR and to
raise FP exceptions.

gcc/
	* config/aarch64/aarch64-builtins.cc (FLAG_NONE): Rename to...
	(FLAG_DEFAULT): ...this and update all references.
	* config/aarch64/aarch64-simd-builtins.def: Update all references
	here too.
	* config/aarch64/aarch64-simd-pragma-builtins.def: Likewise.