hwc: Disable mixed mode composition for secure videos

Also make sure layer cache is used correctly when
we're not using MDP composition

Bug: 7643563
Change-Id: I4dcd70c2da128b2dcbe0b72dc14031983649719d
Signed-off-by: Iliyan Malchev <malchev@google.com>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>

libhwcomposer/hwc_mdpcomp.cpp

@@ -264,6 +264,9 @@ bool MDPComp::isDoable(hwc_context_t *ctx, hwc_display_contents_1_t* list) {
         return false;
     }
 
+    if(ctx->mSecureMode)
+        return false;
+
     //Check for skip layers
     if(isSkipPresent(ctx)) {
         ALOGD_IF(isDebug(), "%s: Skip layers are present",__FUNCTION__);