nvptx: Enhance '-march-map=[...]' test cases

This expands upon the one test case added in
commit de0ef044 "[nvptx] Add march-map".

	gcc/testsuite/
	* gcc.target/nvptx/march-map.c: Remove; expanded into...
	* gcc.target/nvptx/march-map=sm_50.c: ... this.
	* gcc.target/nvptx/march-map=sm_30.c: New.
	* gcc.target/nvptx/march-map=sm_32.c: Likewise.
	* gcc.target/nvptx/march-map=sm_35.c: Likewise.
	* gcc.target/nvptx/march-map=sm_37.c: Likewise.
	* gcc.target/nvptx/march-map=sm_52.c: Likewise.
	* gcc.target/nvptx/march-map=sm_53.c: Likewise.
	* gcc.target/nvptx/march-map=sm_60.c: Likewise.
	* gcc.target/nvptx/march-map=sm_61.c: Likewise.
	* gcc.target/nvptx/march-map=sm_62.c: Likewise.
	* gcc.target/nvptx/march-map=sm_70.c: Likewise.
	* gcc.target/nvptx/march-map=sm_72.c: Likewise.
	* gcc.target/nvptx/march-map=sm_75.c: Likewise.
	* gcc.target/nvptx/march-map=sm_80.c: Likewise.
	* gcc.target/nvptx/march-map=sm_86.c: Likewise.
	* gcc.target/nvptx/march-map=sm_87.c: Likewise.
	* gcc.target/nvptx/march-map=sm_89.c: Likewise.
	* gcc.target/nvptx/march-map=sm_90.c: Likewise.
	* gcc.target/nvptx/march-map=sm_90a.c: Likewise.
	* gcc.target/nvptx/main.c: Remove.