[nvptx] Address genrecog warnings

[nvptx] Address genrecog warnings

    build/genrecog [...]/source-gcc/gcc/common.md [...]/source-gcc/gcc/config/nvptx/nvptx.md \
              insn-conditions.md > tmp-recog.c
    [...]/source-gcc/gcc/config/nvptx/nvptx.md:1206: warning: operand 0 missing mode?
    [...]/source-gcc/gcc/config/nvptx/nvptx.md:1206: warning: operand 1 missing mode?

	gcc/
	* config/nvptx/nvptx.md (allocate_stack): Rename to...
	(allocate_stack_<mode>): ... this, and add :P on both
	match_operand and unspec.
	(allocate_stack): New expander.

From-SVN: r224641