Currently, the non-overlapping video memory carveout region is cleared after
disabling the MMU at EL3. If at any exception level the carveout region is being
marked as cacheable, this zeroing of memory will not have an affect on the
cached lines. Hence, we first invalidate the dirty lines and update the memory
and invalidate again so that both caches and memory is zeroed out.

Change-Id: If3b2d139ab7227f6799c0911d59e079849dc86aa