gralloc: Do not map framebuffer memory unless needed

The SurfaceFlinger opens the framebuffer module even when it
isn't necessary. It does this for some legacy hals.
Due to this we unnecessarily mmap the fb memory in gralloc.
Do not map this unless the property to use the framebuffer
memory is set.

Change-Id: Ib4ebfdf9a63af0dabb53170342181bac0360baeb
1 file changed