add the possibility to document `bind_interrupts` `struct`s

the `bind_interrupts` macro creates a `struct` for the interrupts. it
was so far not possible to document those (except for STM32) and there
was no generic documentation being generated/added either, thus the
`missing_docs` lint was triggered for consumers which enabled it.

with this change it is now possible to manually add a comment on the
`struct` being defined in the macro invocation.

to show that this works one RP example has been modified accordingly.

Both blocking and async versions are supported. Add separate examples
for each mode.

Allow for the use of the OS Event timer as a time source.

Signed-off-by: Felipe Balbi <febalbi@microsoft.com>