gdb: Add tracepoint support for powerpc.

gdb: Add tracepoint support for powerpc.

gdb/gdbserver/ChangeLog:

	* linux-ppc-low.c (ppc_supports_tracepoints): New function.
	(struct linux_target_ops): Wire in the above.

gdb/testsuite/ChangeLog:

	* gdb.trace/ftrace.exp: Set arg0exp for ppc.
	* gdb.trace/mi-trace-unavailable.exp: Set pcnum for ppc.
	* gdb.trace/pending.exp: Accept leading dot before function name.
	* gdb.trace/trace-common.h: Add fast tracepoint dummy insn for ppc.
	* lib/trace-support.exp: Set registers for ppc.