proc/meminfo: include offlined region for mem total

When memory block is logically offlined, it is still part of System RAM
but is inactive, and can be made active or Onlined anytime. Though from
the perspective of kernel which is giving the “current usable memory in
the system" info to userspace via MemTotal, when active-mode memory
onlining is enabled, the offlined blocks can be onlined when there is
memory pressure (on demand) and thus can be added as part of total
available memory in the system.

Change-Id: I3d6acbe5b05c33c60ac3f1346977f5a72e4d5897
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>