bcm2835-i2s: add 24bit support, update bclk_ratio to more correct values

Code ported from bcm2708-i2s driver in Raspberry Pi tree.

RPi commit 62c05a0b ("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>

RPi commit 3e8c672b ("bcm2708-i2s:
Update bclk_ratio to more correct values")

Discussion about blck_ratio affecting sound quality:
https://github.com/raspberrypi/linux/issues/681



Signed-off-by: Matthias Reichl <hias@horus.com>