This patch adds a hint to users for how to set
CONFIG_ZTIMER_USEC_ADJUST_SLEEP. The doc for
CONFIG_ZTIMER_USEC_ADJUST_SET already contained a similar hint.
MSEC and SEC are now usable on TIMER(0) without having USEC
pm is configured by used hardware
OLD configuration values are translated for backward compatibility
prefer rtt for ZTIMER_SEC
avoid doing partial ztimer setup if auto_init_ztimer is disabled
before this patch some const pointers might have been definend to values
that a user who disables auto_init for ztimer does not like.
