shmbridge: Change the bridge size according to dtsi entry

For MDMs, LEVMs and targets other than MSMs, we might not
need to register memory as large as 4M for shmbridge.
This change helps to decide the shmbridge pool size according
to the dtsi entry of the target.

Change-Id: I8f6905b5793f2dbe69f269a05cbbe74855eab708
Signed-off-by: Anmolpreet Kaur <anmolpre@codeaurora.org>