orion_spi: handle 88F6183 erratum

Add support to orion_spi for the 88F6183 ARM SoC by adding code to work
around a 6183-specific erratum.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>