lmkd: mlock all memory

Use mlockall(MCL_FUTURE) to lock all lmkd pages in memory.  This
avoids lmkd thrashing when the system is low on memory.

As a side effect, it will also keep the .text sections of liblog, libm,
libc, and libprocessgroup in memory at all times.

Bug: 16236289
Change-Id: Idd70557efa4b1e14bc86f14220672a30f6c956e3