i2c: add bcm2835 driver

This implements a very basic I2C host driver for the BCM2835 SoC. Missing
features so far are:

* Clock rate adjustment.
* 10-bit addressing.
* DMA.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
clk: bcm2835: probe for fixed-clock in device tree

This will allow fixed-clocks to be registered in device tree, which in
turn will allow clock clients to look up their clocks in device tree.
The first driver to use this feature will be the bcm2835 SDHCI/MMC
driver. In the long run, it is likely these fixed clocks will be
replaced with an actual clock implementation which speaks to the
VideoCore processor, but this change should be transparent to clock
consumers.

Cc: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm2835: add a pm_power_off implementation

Add a pm_power_off function that resets the SoC, and indicates to
bootcode.bin not to boot. Should allow a lower power 'off' state, even
if it's not really off.

This is commit 48efdd2 "Add a pm_power_off function that resets us, ..."
downstream.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
[swarren: Various non-semantic rework for upstreaming]
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm2835 rpi: remove hard-coded memreserve from DT

The Raspberry Pi has either 256MB or 512MB of RAM. However, a portion is
reserved for use by the VideoCore co-processor. The RPi DT contained a
/memreserve/ statement to reserve that RAM. However, the exact amount of
RAM used by the VideoCore is dynamic at boot-time; a firmware config
file specifies the amount. As such, we can't hard-code the size in the
DT. Remove the /memreserve/ statement. The bootloader is expected to
adjust the /memory properties to reflect the RAM size the ARM CPU can
use. Upstream U-Boot certainly does this, although I'm not sure that the
basic firmware does if it boots the kernel directly; users may need to
manually adjust their DT if not using U-Boot.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm2835: add SDHCI node to DT

Add the SDHCI device node to the SoC DT file. Add a dummy fixed-clock
to satisfy the SDHCI driver's clock lookup; eventually this should be
replaced by a real clock implementation. Add board specific properties
to the Raspberry Pi board file.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
ARM: bcm2835: add I2C controllers to DT

The BCM2835 has 3 identical I2C controllers. Instantiate them all in the
SoC .dtsi file, and enable the relevant two in the Raspberry Pi board
.dts file.

Note that on the Raspberry Pi Model B revision 1, I2C0 is connected to
the general-purpose expansion header, and I2C1 is connected to the camera
connector. Revision 2 of the board swaps these assignments:-(

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

Now that we have an SDHCI driver, enable the block layer, and common
filesystems; MSDOS/VFAT for the SoC-required firmware partition, ext2/3/4
for a root partition.

Add tmpfs, NFS, file locking, file notify, networking, and NLS to support
distro expectations.

Enable GPIO_SYSFS to allow GPIO twiddling from user-space; likely a
common activity on this hardware.

Enable I2C.

Remove bogus CONFIG_DEFAULT_MMAP_MIN_ADDR so that applications running as
non-root actually work; without this, execve() immediately triggers
SIGKILL. This setting was sourced from some downstream defconfig early
during upstream Raspberry Pi support development.

Other non-semantic diffs due to rebuilding defconfig using the latest
Kconfig defaults etc.

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