m68k: Add -mlra

	PR target/113939
	* config/m68k/m68k.opt (mlra): New target option.
	* config/m68k/m68k.cc (m68k_use_lra_p): New function.
	(TARGET_LRA_P): Use it.
	* config/m68k/m68k.opt.urls: Regenerate.