nvptx: Restructure code generating function map labels

This restructures the code generating FUNC_MAP and IND_FUNC_MAP labels
in the assembly code for mkoffload to consume, hopefully making it a
bit clearer and easier to search for.

2024-01-03  Kwok Cheung Yeung  <kcy@codesourcery.com>

	gcc/
	* config/nvptx/nvptx.cc (nvptx_record_offload_symbol): Restucture
	printing of FUNC_MAP/IND_FUNC_MAP labels.