memshare: Perform Hypervisor mapping for boot-time allotted memory

The patch performs Hypervisor mapping for guaranteed memshare
client's alloted memory at boot time and prevent allocation
for clients with size zero.

CRs-Fixed: 2062478
Change-Id: I96cc7b2014693d97f11411a7b62d2c365f21caf1
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>