[nvptx] Fix missing mode warnings in nvptx.md, omp part

[nvptx] Fix missing mode warnings in nvptx.md, omp part

Fix these warnings:
...
gcc/config/nvptx/nvptx.md:1074:1: warning: operand 0 missing mode?
gcc/config/nvptx/nvptx.md:1240:1: warning: operand 0 missing mode?
gcc/config/nvptx/nvptx.md:1240:1: warning: operand 1 missing mode?
gcc/config/nvptx/nvptx.md:1240:1: warning: operand 2 missing mode?
gcc/config/nvptx/nvptx.md:1268:1: warning: operand 0 missing mode?
...

Build and reg-tested on x86_64 with nvptx accelerator.

2019-06-17  Tom de Vries  <tdevries@suse.de>

	* config/nvptx/nvptx-protos.h (gen_set_softstack_insn): Declare.
	* config/nvptx/nvptx.c (gen_set_softstack_insn): New function.
	* config/nvptx/nvptx.md (define_insn "set_softstack_insn"): Rename to
	...
	(define_insn "set_softstack_<mode>"): ... this.  Use P iterator on
	match_operand 0.
	(define_insn "omp_simt_enter_insn"): Rename to ...
	(define_insn "omp_simt_enter_<mode>"): ... this.  Use P iterator on
	match_operand 0, 1 and 2, as well as the unspec_volatile result.
	(define_expand "omp_simt_enter): Use gen_omp_simt_enter_di and
	gen_omp_simt_enter_si.
	(define_expand "omp_simt_exit"): New.
	(define_insn "omp_simt_exit"): Rename to ...
	(define_insn "omp_simt_exit_<mode>"): ... this.  Use P iterator on
	match_operand 0.

From-SVN: r272388