powerpc/85xx: p1022ds: enable monitor switching via pixis indirect mode

When the P1022's DIU video controller is active, the pixis must be accessed
in "indirect" mode, which uses localbus chip select addresses.

Switching between the DVI and LVDS monitor ports is handled by the pixis,
so that switching needs to be done via indirect mode.

This has the side-effect of no longer requiring U-Boot to enable the DIU.
Now Linux can enable the DIU all by itself.

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