msm: memory: remove obsolete stable_size function

The notion of `stable' memory is going away (i.e. all memory is now
treated as `stable'). Remove the stable_size function. Remove the
notion of stability from the total_stable_size function and rename it
to total_size.

Change-Id: I8fd08a36b4948d57f430aea9113a0c704b8a00d0
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>