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
1 file changed