powerpc/85xx: add pixis indirect mode device tree node

The Freescale P1022 has a unique pin muxing "feature" where the DIU video
controller's video signals are muxed with 24 of the local bus address signals.
When the DIU is enabled, the bulk of the local bus is disabled, preventing
access to memory-mapped devices like NOR flash and the pixis FPGA.

In this situation, the pixis supports "indirect mode", which allows access
to the pixis itself by reading/writing addresses on specific local bus
chip selects.  CS0 is used to select which pixis register to access, and
CS1 is used to read/write the value.

To support this, we introduce another board-control child node of the
localbus node that contains a 'reg' property for CS0 and CS1.  This will
produce the correct physical addresses for CS0 and CS1.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>