hw/mcu/dialog: Add callbacks on enter/exit sleep

[andrzej-kaczmarek]

This patch adds callbacks to be called before and after deep sleep. Those are intended to be registered by BSP which can then decide to save/restore state of certain peripherals and release/acquire power domains in order to save some power while M33 goes into deep sleep.

Note that similar power saving can usually be achieved if application uses os_dev_open/close consistently, i.e. opens device only when needed, which should properly acquire and release power domains (although the actual behavior depends on a driver implementation). However, there may still be some cases where quick save/restore is possible and this can be handled in new callbacks.

[apache-mynewt-bot]

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