msm: mdp: Free secure memory based on pipe config

When there is no secure pipe configured, we can unmap secure
memory instead of relying on unset with secure flag set from
userspace.

Bug: 11857675

Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>

idea is taken here - https://github.com/hellsgod/kernel_msm/commit/1b766b563309d00b0767020d92b8abb3a1cf9f85