tests/drivers/rtc/rtc_api_helpers: Test for more archs

The test suite was limited to the native_posix board,
now it is built and run for any board supported by CI.

The native_posix yaml files for both 32 and 64 bit
boards have been expanded to support rtc, allowing CI
to build and test the rtc_api test suite against the
native_posix and native_posix_64 boards.

Signed-off-by: Bjarki Arge Andreasen <baa@trackunit.com>