Treat all unknown auxv tags on FreeBSD as unknown.

Treat all unknown auxv tags on FreeBSD as unknown.

Previously, default_print_auxv_entry was called for any auxv entries
without a known AT_FREEBSD_* tag.  However, this resulted in false
positive matches when FreeBSD added a new tag that has an existing
AT_* tag with a different meaning.  Instead, only call
default_print_auxv_entry for specific tag values for which FreeBSD
matches the default AT_* values.

gdb/ChangeLog:

	* fbsd-tdep.c (fbsd_print_auxv_entry): Only use
	default_print_auxv_entry for specific tag values.