ARM: bm2835: fix I2C module clock rate

BCM2835-ARM-Peripherals.pdf states that the I2C module's input clock is
nominally 150MHz, and that value is currently reflected in bcm2835.dtsi.
However, practical measurements show that the rate is actually 250MHz,
and this agrees with various downstream kernels.

Switch the I2C clock's frequency to 250MHz so that the generated bus
clock rate is accurate.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
spi: add driver for BCM2835

The BCM2835 contains two forms of SPI master controller (one known
simply as SPI0, and the other known as the "Universal SPI Master", in
the auxilliary block) and one form of SPI slave controller. This patch
adds support for the SPI0 controller.

This driver is taken from Chris Boot's repository at
git://github.com/bootc/linux.git rpi-linear
as of commit 6de2905 "spi-bcm2708: fix printf with spurious %s".
In the first SPI-related commit there, Chris wrote:

Thanks to csoutreach / A Robinson for his driver which I used as an
inspiration. You can find his version here:
http://piface.openlx.org.uk/raspberry-pi-spi-kernel-driver-available-for

Changes made during upstreaming:
* Renamed bcm2708 to bcm2835 as per upstream naming for this SoC.
* Wrote device tree binding documentation.
* Request unnamed clock rather than "sys_pclk"; the DT will provide the
  correct clock.
* Assume that tfr->speed_hz and tfr->bits_per_word are always set in
  bcm2835_spi_start_transfer(), bcm2835_spi_transfer_one(), so no need
  to check spi->speed_hz or tft->bits_per_word.
* Re-ordered probe() to remove the need for temporary variables.
* Don't use devm_request_irq(), to ensure that the IRQ doesn't fire after
  we've torn down the device, but not unhooked the IRQ.
* Removed empty prepare/unprepare implementations.
* Removed use of devinit/devexit.
* Added BCM2835_ prefix to defines.

Signed-off-by: Chris Boot <bootc@bootc.net>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm2835: add SPI device to DT

FIXME: describe more, check actual rate of dummy clock.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm2835: defconfig update

Enable the new SPI controller driver.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
LOCAL HACK: ARM: bcm2835: enable enc28j60 SPI device

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>