memshare: Restructuring memshare as a driver

Currently, memshare is implemented as a module. This patch
restructures the design of memshare and converts it to a
device tree dependent driver.

Change-Id: I85734cfd832da058a725a59980f81b835f85aeb9
Signed-off-by: Katish Paran <kparan@codeaurora.org>