lowmem: Rename structure and functions of controller ops

lowmem: Rename structure and functions of controller ops

For unity, structure for storing governor/controller and related
functions to it were renamed.

Big rules:
 * initialize -> register
 * controller_ops -> mem_level_ops
 * action -> controller

Details are below:
 * Registering(init) functions
    * lowmem_initialize_... -> lowmem_register_...
    * lowmem_..._governor_ops -> lowmem_..._lmk_governor
    * lowmem_..._kill_candidates -> lowmem_..._lmk_controller
    * lowmem_..._controller_ops_... -> lowmem_..._mem_level_...
    * lowmem_..._action -> lowmem_..._controller
 * Structure
    * struct lowmem_controller_ops -> structure lowmem_mem_level_ops
    * action -> controller
      (member of lowmem_mem_level_ops)
    * lowmem_actions[MEM_LEVEL_MAX] -> mem_level_ops_list[MEM_LEVEL_MAX]
      (declaration of 'struct lowmem_mem_level_ops')
 * Governor function
    * oom_mem_governor -> mem_state_oom_governor
      (for unity, since dummy governor is mem_state_dummy_governor)

Change-Id: Ieb03b2ced71dd4826fbedc75cc333215b8d20193
Signed-off-by: SangYoun Kwak <sy.kwak@samsung.com>