spi_mpc83xx: much improved driver

The current driver may cause glitches on SPI CLK line since one must disable
the SPI controller before changing any HW settings.  Fix this by implementing
a local spi_transfer function that won't change speed and/or word size while
CS is active.

While doing that heavy lifting a few other issues were addressed too:
 - Make word size 16 and 32 work too.
 - Honor bits_per_word and speed_hz in spi transaction.
 - Optimize the common path.

This also stops using the "bitbang" framework (except for a few constants).

[Roel Kluin <12o3l@tiscali.nl>: "irq" needs to be signed]
Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
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>

drivers/spi/Kconfig

@@ -126,7 +126,6 @@ config SPI_MPC52xx_PSC
 config SPI_MPC83xx
 	tristate "Freescale MPC83xx/QUICC Engine SPI controller"
 	depends on SPI_MASTER && (PPC_83xx || QUICC_ENGINE) && EXPERIMENTAL
-	select SPI_BITBANG
 	help
 	  This enables using the Freescale MPC83xx and QUICC Engine SPI
 	  controllers in master mode.