AVR: target/107201: Make -nodevicelib work for all devices.

AVR: target/107201: Make -nodevicelib work for all devices.

	driver-avr.cc contains a spec that discriminates bwtween cores
	and devices by means of a mmcu=avr* spec pattern.  This does not
	work for new devices like AVR128* which also start with mmcu=avr
	like all cores do.  The patch uses a new spec function in order to
	tell apart cores from devices.

gcc/
	PR target/107201
	* config/avr/avr.h (EXTRA_SPEC_FUNCTIONS): Add no-devlib, avr_no_devlib.
	* config/avr/driver-avr.cc (avr_no_devlib): New function.
	(avr_devicespecs_file): Use it to remove -nodevicelib from the
	options for cores only.
	* config/avr/avr-arch.h (avr_get_parch): New prototype.
	* config/avr/avr-devices.cc (avr_get_parch): New function.