event: Convert misc_init_f() to use events

This hook can be implmented using events, for the three boards that
actually use it.

Add the event type and event handlers. Drop CONFIG_MISC_INIT_F since we
can just use CONFIG_EVENT to control this. Since sandbox always enables
CONFIG_EVENT, we can drop the defconfig lines there too.

Signed-off-by: Simon Glass <sjg@chromium.org>