spi: remove completely broken Tegra driver

The current SPI driver has many issues. Examples are:

* Segfaulting on most transfers due to expecting all transfers to have
  both RX and TX buffers.
* Hanging on TX transfers since the whole driver flow is driven by RX
  DMA completion, but the HW is only told to enable RX for RX transfers.
* Use of clk_disable_unprepare() from atomic context.
* Once those and other minor issues are fixed, the driver still doesn't
  actually work.
* The driver also implements a deprecated API to the SPI core.

For this reason, simply remove the driver completely. This has two
advantages:

1) This will remove the last use of Tegra's <mach/dma.h>, which will
   allow that file to be removed, which is required for single zImage
   work.

2) The downstream driver is significaly different from the current
   code. I believe a patch to re-add the downstream driver (with
   appropriate cleanup) will be much simpler to review if it's a new
   file rather than randomly interspered with essentially unrelated
   existing code.
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/spi/Kconfig

@@ -377,12 +377,6 @@ config SPI_MXS
 	help
 	  SPI driver for Freescale MXS devices.
 
-config SPI_TEGRA
-	tristate "Nvidia Tegra SPI controller"
-	depends on ARCH_TEGRA && (TEGRA_SYSTEM_DMA || TEGRA20_APB_DMA)
-	help
-	  SPI driver for NVidia Tegra SoCs
-
 config SPI_TI_SSP
 	tristate "TI Sequencer Serial Port - SPI Support"
 	depends on MFD_TI_SSP

drivers/spi/Makefile

@@ -59,7 +59,6 @@ obj-$(CONFIG_SPI_SH_MSIOF)		+= spi-sh-msiof.o
 obj-$(CONFIG_SPI_SH_SCI)		+= spi-sh-sci.o
 obj-$(CONFIG_SPI_SIRF)		+= spi-sirf.o
 obj-$(CONFIG_SPI_STMP3XXX)		+= spi-stmp.o
-obj-$(CONFIG_SPI_TEGRA)			+= spi-tegra.o
 obj-$(CONFIG_SPI_TI_SSP)		+= spi-ti-ssp.o
 obj-$(CONFIG_SPI_TLE62X0)		+= spi-tle62x0.o
 obj-$(CONFIG_SPI_TOPCLIFF_PCH)		+= spi-topcliff-pch.o