Camera: Adding support to change preview size based on picture size

Added 768x432 preview size for 16:9 picture aspect ratio. This size is
chosen as it is lesser than WVGA and therefore will not require increase
in pmem and the height is a multiple of 16.
Clearing PostView heap in initPreview for 7x30 as preview size changes
based on picture size aspect ratio

CRs-Fixed: 227167
diff --git a/QualcommCameraHardware.cpp b/QualcommCameraHardware.cpp
index 1c8575d..4b81112 100644
--- a/QualcommCameraHardware.cpp
+++ b/QualcommCameraHardware.cpp
@@ -164,6 +164,7 @@
 static const camera_size_type preview_sizes[] = {
     { 1280, 720 }, // 720P, reserved
     { 800, 480 }, // WVGA
+    { 768, 432 },
     { 720, 480 },
     { 640, 480 }, // VGA
     { 576, 432 },
@@ -2004,6 +2005,7 @@
         return false;
     }
     if( mCurrentTarget == TARGET_MSM7630 ) {
+        mPostViewHeap.clear();
 	if(mPostViewHeap == NULL) {
 	    LOGV(" Allocating Postview heap ");
 	    /* mPostViewHeap should be declared only for 7630 target */