Switch zram management based on mmd AConfig flag and mmd.zram.enabled system property

During launch of mmd, Android devices has 2 systems for zram management
which are mutally exclusive: mmd and old system (swapon_all +
ZramWriteback.java in system_server).

MmdProperties.mmd_zram_enabled() is the wrapper API for the
"mmd.zram.enabled" system property.

If both "mmd_enabled" AConfig flag and "mmd.zram.enabled" system
property are enabled, mmd manages zram. Otherwise the old system manages
zram (though zram may not be utilized on the device).

This also pushes refreshZramSettings() to the another branch from mmd
because mmd system does not support enabling zram via Settings for
experiments.

Bug: 393481329
Test: manual

Change-Id: Ied2a36a3cddd4fe7936b5476c05d3442ec439431