soc: fsl: cpm1: qmc: Introduce available timeslots masks

Available timeslots masks define timeslots available for the related
channel. These timeslots are defined by the QMC binding.

Timeslots used are initialized to available timeslots but can be a
subset of available timeslots.
This prepares the dynamic timeslots management (ie. changing timeslots
at runtime).

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20231205152116.122512-8-herve.codina@bootlin.com