ARM: sunxi: Update datasheet documentation

We have access to more documentation now, especially the user manuals,
so add the links to them, and do so minor comestic changes while we're
at it.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
ARM: sunxi: irqchip: Update the documentation

A10 and A13 have a different set of available interrupt sources, reflect
this in the documentation.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>