sunxi: Rename cpu.h to cpu_sun4i.h

sun4i - sun8i have (aprox.) the same iomem layout, but sun9i is quite
different, so add a wrapper cpu.h which includes the right mach specific
cpu_sun#i.h based on mach, like we already do with clock.h and dram.h .

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>