dt-bindings: arm: amlogic: fix x96-max/sei510 section in amlogic.yaml

Move amediatech,x96-max and seirobotics,sei510 to the S905D2 section and
update the S905D2 description to S905D2/X2/Y2.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>