Now, the A83T and A64 SoC user manuals are available.
Update the documentation to add the links.

An updated version of A83T datasheet is also included now.
Signed-off-by: NIcenowy Zheng <icenowy@aosc.xyz>
Acked-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>