ASoC: Add support for BCM2708

This driver adds support for digital audio (I2S)
for the BCM2708 SoC that is used by the
Raspberry Pi. External audio codecs can be
connected to the Raspberry Pi via P5 header.

It relies on cyclic DMA engine support for BCM2708.

Signed-off-by: Florian Meier <florian.meier@koalo.de>

ASoC: BCM2708: Add 24 bit support

This adds 24 bit support to the I2S driver of the BCM2708.
Besides enabling the 24 bit flags, it includes two bug fixes:

MMAP is not supported. Claiming this leads to strange issues
when the format of driver and file do not match.

The datasheet states that the width extension bit should be set
for widths greater than 24, but greater or equal would be correct.
This follows from the definition of the width field.

Signed-off-by: Florian Meier <florian.meier@koalo.de>

bcm2708-i2s: Update bclk_ratio to more correct values

Move GPIO setup to hw_params.

This is used to stop the I2S driver from breaking
the GPIO setup for other uses of the PCM interface

Configure GPIOs for I2S based on revision/card settings

With RPi model B+, assignment of the I2S GPIO pins has changed.
This patch uses the board revision to auto-detect the GPIOs used
for I2S. It also allows sound card drivers to set the GPIOs that
should be used. This is especially important with the Compute
Module.

bcm2708-i2s: Avoid leak from iomap when accessing gpio

bcm2708: Eliminate i2s debugfs directory error

Qualify the two regmap ranges uses by bcm2708-i2s ('-i2s' and '-clk')
to avoid the name clash when registering debugfs entries.