Patch from George G. Davis

Use ARMv6 supersections for 16MiB static kernel direct mapped memory
regions when possible.
Based on comments received for the first version of this patch, this
version has added a comment to clarify that ARMv6 supersections are
only valid for the domain == 0 case and moved the supersection address
mask and size macros before the hardware page table definitions.

Signed-off-by: George G. Davis
Signed-off-by: Russell King