Move shared code from mpc5121_ads.c to new file mpc512x_shared.c
- mpc512x_find_ips_freq -> unchanged
- contents of mpc5121_ads_init_IRQ -> mpc512x_init_IRQ
  - looking for fsl,mpc5121-ipic instead of fsl,ipic
- mpc5121_ads_declare_of_platform_devices -> mpc5121_declare_of_platform_devices
  - and use compatible for lookup instead of node name

Add new generic board setup mpc5121_generic.c
Signed-off-by: NJohn Rigby <jrigby@freescale.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

512x is very similar to 83xx and most
of this is patterned after code from 83xx.

New platform:
    changed:
	arch/powerpc/Kconfig
	arch/powerpc/platforms/Kconfig
	arch/powerpc/platforms/Kconfig.cputype
	arch/powerpc/platforms/Makefile
    new:
	arch/powerpc/platforms/512x/*
	include/asm-powerpc/mpc512x.h
Signed-off-by: NJohn Rigby <jrigby@freescale.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>