fmem: interact properly with DMM

On a system with both FMEM and DMM, FMEM must veto
memory hotremove of section(s) FMEM occupies when
in C-state and allow it (after cleaning up metadata)
in T-state (and then change to O-state).

It must also change back to T-state when all sections
FMEM uses have been powered on.

Change-Id: I9766a07305d1e3e2c6ff48e1cbf6933765b751f8
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>