tests: drivers: uart: Re-enabling some tests on nrf52_bsim

Tests which were using the new nordic UART shim where failing
on the bsim targets. They are now fixed and tests can be
re-enabled.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>
(cherry picked from commit 362389ee170115149fad78090f72eed80486f6c3)
2 files changed