aarch64: Reintroduce FLAG_AUTO_FP

aarch64: Reintroduce FLAG_AUTO_FP

The flag now known as FLAG_QUIET is an odd-one-out in that it
removes side-effects rather than adding them.  This patch inverts
it and gives it the old name FLAG_AUTO_FP.  FLAG_QUIET now means
"no flags" instead.

gcc/
	* config/aarch64/aarch64-builtins.cc (FLAG_QUIET): Redefine to 0,
	replacing the old flag with...
	(FLAG_AUTO_FP): ...this.
	(FLAG_DEFAULT): Redefine to FLAG_AUTO_FP.
	(aarch64_call_properties): Update accordingly.