lmkd: only mlockall() if enabled

Move process initialization, mlockall() and sched_setscheduler() to
only occur if initialization succeeds and is enabled.  This
conserves mlock'd memory and a FIFO processing slot if (deprecated)
kernel lowmemorykiller is active.

Cleanup: Android coding standard compliance.

Test: lmkd_unit_test
Bug: 33808187
Bug: 72838192
Change-Id: I51af0235c8eca4ef958ef2d83a8071ff58b49d78