aarch64: Enable DFP (Decimal Floating-point) (BID format)

This patch enables DFP support on aarch64, by updating config/dfp.m4
and regenerating the involved configure scripts.
We enable the BID format.

2022-03-31  Christophe Lyon  <christophe.lyon@arm.com>

	config/
	* dfp.m4: Add aarch64 support.
	gcc/
	* configure: Regenerate.
	libdecnumber/
	* configure: Regenerate.
	libgcc/
	* configure: Regenerate.