documentation: arm: sunxi: Allwinner H2+/H3 update

Replaced the link to the datasheet by a link to the current version.

Signed-off-by: Wilken Gottwalt <wilken.gottwalt@mailbox.org>
Link: https://lore.kernel.org/r/20200923065954.GA22809@monster.powergraphx.local


Signed-off-by: Jonathan Corbet <corbet@lwn.net>