gas: ginsn: do not emit an unnecessary trailing comma in textual dump

For ginsns with less than 2 source operands or no destination operands,
the current textual dump contains a superfluous comma, like the relevant
testcases show.

Adjust the code a bit to not emit the lone trailing comma.  Also, adjust
the aarch64 and x86_64 testcases.

gas/
        * ginsn.c (ginsn_src_print): Do not use a trailing comma when
	printing the src of ginsn.
        (ginsn_print): Check the strlen and prefix a comma before the
	src string.

gas/testsuite/
	* gas/scfi/aarch64/ginsn-cofi-1.l: Adjust the expected textual
	dump of the ginsn.
	* gas/scfi/x86_64/ginsn-cofi-1.l: Likewise.
3 files changed