boards: emsdp,hsdk: drop GPIO_INIT_PRIORITY overrides

These were also added as part of some major refactoring and should not
be relevant anymore. They are also the last two GPIO_INIT_PRIORITY
overrides left in boards, so after this every GPIO device should be
working with the standard initialization priority.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>