AVR: target/125752 - Add 64-bit fixed point <-> 64-bit double conversions.

	PR target/125752
libgcc/config/avr/libf7/
	* libf7-asm.sx (ufx64_to_d, d_to_fx64): New DEFUNs.
	(__fractdadf, __fractudadf, __fracttadf, __fractutadf)
	(__fractdqdf, __fractudqdf): New _DEFUNs.
	* libf7-common.mk (F7_ASM_PARTS) Add: fx2D, D2fx,
	dq2D, udq2D, da2D, uda2D, ta2D uta2D.
	(F7F): Add d_to_fx64, ufx64_to_d, sfx64_to_d.
	* libf7.c (d_to_ufx, d_to_sfx): New protos.
	(__fractdfda, __fractdfuda, __fractdfta, __fractdfuta)
	(__fractdfdq, __fractdfudq): New modules.
	* t-libf7 (LIBF7_DF_CONV): Add fractdfda,
	fractdfta, fractdfdq, fractdfuda, fractdfuta, fractdfudq.
	* f7-renames.h: Rebuild.

gcc/testsuite/
	* gcc.target/avr/torture/fx-to-double.c: New test.