perf: Split out arch specific code & improve PowerPC perf probe support

[Ian Munsie]

These patches add the required mappings to use perf probe on PowerPC.

Functionality wise it requires the patch titled "powerpc: Add kprobe-based
event tracer" from the powerpc-next tree to provide the
HAVE_REGS_AND_STACK_ACCESS_API required for CONFIG_KPROBE_EVENT. The code will
still compile cleanly without it and will fail gracefully at runtime on the
missing CONFIG_KPROBE_EVENT support as before.

Part 1 of the patch series moves the arch dependent x86 32 and 64 bit DWARF
register number mappings out into a separate arch directory and adds the
necessary Makefile foo to use it.

Part 2 of the patch series adds the PowerPC mappings.


Changes since v1: From Masami Hiramatsu's suggestion, I added a check in the
Makefile for if the arch specific Makefile defines PERF_HAVE_DWARF_REGS,
printing a message during build if it has not. This simplifies the code
removing the odd macro from the previous version and the need for an arch
specific arch_dwarf-regs.h. I have not entirely disabled DWARF support for
architectures that don't implement the register mappings, so that they can
still add a probe based on a line number (they will be missing the ability to
capture the value of a variable from a register).


Thanks,
-Ian