module: Add a new entry to the priority of modules

module: Add a new entry to the priority of modules

A new entry, MODULE_PRIORITY_INITIAL is added to the enum of
module_priority.

This priority is added for the reason below:
 * Since the 'lowmem' module has MODULE_PRIORITY_EARLY as its priority,
   modules separated from 'lowmem' module should be initialized before
   MODULE_PRIORITY_HIGH but after MODULE_PRIORITY_EARLY.

Thus, the newly added priority MODULE_PRIORITY_INITIAL will be used by
modules which need to be initialized before all other modules but after
MODULE_PRIORITY_EARLY.

Change-Id: I07f31f05c5b8851de14a8461504ce04784b6722f
Signed-off-by: SangYoun Kwak <sy.kwak@samsung.com>