ASoC: tegra20: i2s: Add reset control

The I2S reset may be asserted at a boot time, in particular this is the
case on Tegra20 AC100 netbook. Tegra20 I2S driver doesn't manage the
reset control and currently it happens to work because reset is implicitly
deasserted by the tegra-clk driver when I2S clock is enabled. The I2S
permanently stays in a reset once tegra-clk is fixed to not touch the
resets, which it shouldn't be doing. Add reset control to the Tegra20
I2S driver.

Note that I2S reset was always specified in Tegra20 device-tree, hence
DTB ABI changes aren't required.

Tested-by: Paul Fertser <fercerpav@gmail.com> # T20 AC100
Reported-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20210314154459.15375-3-digetx@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>