powerpc: Remove arch/ppc and include/asm-ppc

All the maintained platforms are now in arch/powerpc, so the old
arch/ppc stuff can now go away.

Acked-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Becky Bruce <becky.bruce@freescale.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Jochen Friedrich <jochen@scram.de>
Acked-by: John Linn <john.linn@xilinx.com>
Acked-by: Jon Loeliger <jdl@freescale.com>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Acked-by: Scott Wood <scottwood@freescale.com>
Acked-by: Sean MacLennan <smaclennan@pikatech.com>
Acked-by: Segher Boessenkool <segher@kernel.crashing.org>
Acked-by: Stefan Roese <sr@denx.de>
Acked-by: Stephen Neuendorffer <stephen.neuendorffer@xilinx.com>
Acked-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>