[POWERPC] modify mpc83xx platforms to use new IRQ layer

This fixes MPC834x MDS (formerly SYS) and ITX platform code to get IRQ data (including PCI) from the device tree, and to use the new IPIC code.

renamed defconfig (sys -> mds), left one redundant NULL assignment in mpc83xx_pcibios_fixup to keep the compiler happy.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>