perf probe: Add PowerPC DWARF register number mappings

This adds mappings from the register numbers from DWARF to the
register names used in the PowerPC Regs and Stack Access API.  This
allows perf probe to be used to record variable contents on PowerPC.

This requires the functionality represented by the config symbol
HAVE_REGS_AND_STACK_ACCESS_API in order to function, although it will
compile without it.  That functionality is added for PowerPC in commit
359e4284 ("powerpc: Add kprobe-based event tracer").

Signed-off-by: Ian Munsie <imunsie@au.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>