PR26044, Some targets can't be compiled with GCC 10 (tilepro)

Since this value is used in fields of type tilepro_pipeline (as
NO_PIPELINE, see tc-tilepro.c) it is appropriate to put it in
the tilepro_pipelen enum.  This avoids a warning about converting from
one enum type to another.

	PR 26044
	* opcode/tilepro.h (TILEPRO_NUM_PIPELINE_ENCODINGS): Move to
	tilepro_pipeline enum.