LoongArch: Fix internal error running "gcc -march=native" on LA664

On LA664, the PRID preset is ISA_BASE_LA64V110 but the base architecture
is guessed ISA_BASE_LA64V100.  This causes a warning to be outputed:

    cc1: warning: base architecture 'la64' differs from PRID preset '?'

But we've not set the "?" above in loongarch_isa_base_strings, thus it's
a nullptr and then an ICE is triggered.

Add ISA_BASE_LA64V110 to genopts and initialize
loongarch_isa_base_strings[ISA_BASE_LA64V110] correctly to fix the ICE.
The warning itself will be fixed later.

gcc/ChangeLog:

	* config/loongarch/genopts/loongarch-strings:
	(STR_ISA_BASE_LA64V110): Add.
	* config/loongarch/genopts/loongarch.opt.in:
	(ISA_BASE_LA64V110): Add.
	* config/loongarch/loongarch-def.c
	(loongarch_isa_base_strings): Initialize [ISA_BASE_LA64V110]
	to STR_ISA_BASE_LA64V110.
	* config/loongarch/loongarch.opt: Regenerate.
	* config/loongarch/loongarch-str.h: Regenerate.