powerpc/86xx: add MMC SPI support for MPC8610HPCD boards

This patch adds spi and mmc-spi-slot nodes, plus a gpio-controller for
PIXIS' sdcsr bank that is used for managing SPI chip-select and for
reading card's states.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Cc: Kumar Gala <galak@gate.crashing.org>
Cc: David Brownell <david-b@pacbell.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>