[nvptx] Enable large vectors

[nvptx] Enable large vectors

Allow vector_length clauses to accept values larger than warp size.  Note that
this does not enable setting vector_length to values larger than warp size using
-fopenacc-dim.

2019-01-12  Tom de Vries  <tdevries@suse.de>

	* config/nvptx/nvptx.c (nvptx_goacc_validate_dims): Take larger vector
	lengths into account.

	* testsuite/libgomp.oacc-c-c++-common/vector-length-128-1.c: Expect
	vector length to be 128.
	* testsuite/libgomp.oacc-c-c++-common/parallel-dims.c: Expect vector
	length 2097152 to be reduced to 1024 instead of 32.

From-SVN: r267889