ASoC: stm32: i2s: update pcm hardware constraints

- Set period minimum size. Ensure at least 5ms period
up to 48kHz/16 bits to prevent underrun/overrun.
- Remove MDMA constraints on period maximum size and
set period maximum to half the buffer maximum size.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>