sun6i: Enable SPL

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sun6i: Add initial clock setup for SPL

With this patch and built with SPL,NO_AXP options added, it is possible
to build a non-functional SPL for the A31, which will properly load and
print its banner on the serial console:

U-Boot SPL 2014.04-rc2-01254-g7e81174-dirty (Mar 28 2014 - 21:09:16)
Board: Colombus
sun6i SPL support is not yet complete

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sunxi: Split clock code into common, sun4i and sun6i code

Rather then having effectively 2 copies of a function through
 #ifdef CONFIG_SUN6I ... #else ... #endif, really make 2 copies of the
function in 2 separate C-files, this is much easier to read and maintain.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>