msm: display: fb blend setting via MSMFB_METADATA_SET ioctl

MSMFB_METADATA_SET ioctl is added for the fb user to pass
in additional infomation rather than using reserved
fields.
User can set pre-multiplied alpha for the frame buffer via this
ioctl, overlay blend setting will take this into account.

(cherry picked from commit a2505533d43169288d5508c44ec8ac968a65b82c)

Change-Id: Iba20537a07eeca6a7dffd2910fbc28836ba2f3fa
Signed-off-by: Ken Zhang <kenz@codeaurora.org>
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>