memshare: Boot time allocation and handling multiple clients

Currently, memshare driver is designed to handle single
client. Also there are clients which requires guaranteed memory
from the driver. This patch does the following:

1. Does the boot-time allocation for the clients which does
need guaranteed memory.

2. Provides an infrastructure to handle multiple clients.

3. Created different device nodes for different clients for
calling into DMA api's.

4. On peripheral subystem restart, the memory allocated for the
clients which doesn't need guaranteed memory is freed up.

5. Even upon receiving a free request for a client which requires
guaranteed memory, the memory is not freed up.

Change-Id: I868fde012f3a0771a9bdab07f74c6cb8e710d578
CRs-fixed: 673858
Signed-off-by: Katish Paran <kparan@codeaurora.org>