[ARM] tegra: tegra_i2s_audio: configure in/out buffer sizes from user space

[ARM] tegra: tegra_i2s_audio: configure in/out buffer sizes from user space

-- Add ioctls for configuring buffer, threshold, and DMA-transaction sizes from
   user space.
-- Buffer sizes are provided in orders of magnitude.
-- Allocate max-sized buffers during probe, and allow the user to resize them
   only within the original allocation, to avoid the risk from kmalloc failing
   due to kernel-heap fragmentation, and also to avoid race conditions on DMA
   shut-down.
-- In tegra_audio_write(), moved the call to start_playback_if_necessary()
   immediately after writing to the fifo.  Otherwise, when the fifo size is
   smaller than what the user is trying to write, the user will block before
   playback is started.
-- Silenced printk spew on spinning on i2s registers after transactions are
   completed.
-- Cleaned up a 80-col style violation in downsample()

Signed-off-by: Iliyan Malchev <malchev@google.com>