disp: msm: perform delayed buf attach during secure transitions

While transitioning from secure usecases, the secure
context bank is attached back only during the commit
phase. This leads to invalid secure context-bank device
issue, when the prime_to_fd call is made for the next
frame. Avoid it, by attaching to default drm device
during the prime_to_fd call and reattach it to the
secure context-bank device at the delayed import time.

Change-Id: I43e6da7f117f20746943a48b5f2657e9ae2947ea
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>