msm: mdss: Enable fixed MMBs support for RGB pipes

RGB pipes in some of the chip-sets are statically tied to dedicated
Memory Macro Blocks (MMBs) out of common shared memory pool. These MMBs
cannot be used by other pipes. Enable support for this fixed MMBs by
parsing indexes from device tree and reserving fixed MMBs first before
general pool is used.

Change-Id: Ic4bc7fa790f430a2853719fec7fd849149bc6976
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>