drivers: interrupt_controller: Refactor drivers to use shared init prio

Refactors interrupt controller drivers to use the shared driver class
initialization priority configuration, CONFIG_INTC_INIT_PRIORITY, to
allow configuring interrupt controller drivers separately from other
devices. This is similar to other driver classes.

The default is set to CONFIG_KERNEL_INIT_PRIORITY_DEFAULT to preserve
the existing default initialization priority for most drivers.

Signed-off-by: Maureen Helm <maureen.helm@intel.com>