gdb, doc: Add ieee_half and bfloat16 to list of predefined target types.

For some reason these two weren't added to the list when they were orginally
added to GDB.

gdb/doc/ChangeLog:
2021-09-21  Felix Willgerodt  <felix.willgerodt@intel.com>

	* gdb.texinfo (Predefined Target Types): Mention ieee_half and bfloat16.
1 file changed