disp: fix compilation issue with trusted VM config

This is temporary change to avoid compilation issues on
genericarmv8 recipe. This will be reverted once the
display support is added for the recipe.

Change-Id: I805cf0b98ed77d9d4af72422a2a5b2533658ab73
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>