gdbserver: QTNotes, plug memory leak.

The previous notes aren't being released before setting new ones.

Tested on x86_64 Fedora 17.

gdb/gdbserver/
2013-02-14  Pedro Alves  <palves@redhat.com>

	Plug memory leak.

	* tracepoint.c (cmd_qtnotes): Free TRACING_USER_NAME,
	TRACING_NOTES and TRACING_STOP_NOTE before clobbering.
opcodes/

	* aarch64-opc.c (aarch64_prfops): Change unnamed operation 'name'
	fields to NULL.
	(aarch64_print_operand): Adjust the printing for AARCH64_OPND_PRFOP.

gas/

	* config/tc-aarch64.c (md_begin): Change to check if 'name' is
	NULL.

gas/testsuite/

	* gas/aarch64/system.s: Add tests.
	* gas/aarch64/system.d: Update.