Documentation/rv: Adapt documentation after da_monitor refactoring

Documentation/rv: Adapt documentation after da_monitor refactoring

Previous changes refactored the da_monitor header file to avoid using
macros. This implies a few changes in how to import and use da_monitor
helpers:

 DECLARE_DA_MON_<TYPE>(name, type) is substituted by
 #define RV_MON_TYPE RV_MON_<TYPE>

 da_handle_event_<name>() is substituted by
 da_handle_event()

Update the documentation to reflect the changes.

Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/r/20251126104241.291258-4-gmonaco@redhat.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>