msm: mdss: support FB memory reservation removal on 8x10

User space is allocating its own ION memory for composition
buffer, which makes the FB memory allocation in the driver
redundant.

Change-Id: I79d655bf0dac02fd2c6b9a40dfcc3cc5c6a4343a
Signed-off-by: Radhika Ranjan Soni <rrsoni@codeaurora.org>