[nvptx] Add nvptx-gen.h and nvptx-gen.opt

[nvptx] Add nvptx-gen.h and nvptx-gen.opt

Use nvptx-sm.def to generate new files nvptx-gen.h and nvptx-gen.opt, and:
- include nvptx-gen.h in nvptx.h, and
- add nvptx-gen.opt to extra_options (before nvptx.opt, in case that matters).

Tested on nvptx.

gcc/ChangeLog:

2022-02-25  Tom de Vries  <tdevries@suse.de>

	* config.gcc (nvptx*-*-*): Add nvptx/nvptx-gen.opt to extra_options.
	* config/nvptx/gen-copyright.sh: New file.
	* config/nvptx/gen-h.sh: New file.
	* config/nvptx/gen-opt.sh: New file.
	* config/nvptx/nvptx.h (TARGET_SM35, TARGET_SM53, TARGET_SM70)
	(TARGET_SM75, TARGET_SM80): Move ...
	* config/nvptx/nvptx-gen.h: ... here.  New file, generate.
	* config/nvptx/nvptx.opt (Enum ptx_isa): Move ...
	* config/nvptx/nvptx-gen.opt: ... here.  New file, generate.
	* config/nvptx/t-nvptx ($(srcdir)/config/nvptx/nvptx-gen.h)
	($(srcdir)/config/nvptx/nvptx-gen.opt): New make target.