ARM: dts: meson: add SoC information nodes

The SoC type and version information is encoded in different register
blocks.
The SoC type information is part of the "assist" registers.
The misc version information is part of the "bootrom" registers.
On Meson8, Meson8b and Meson8m2 there is additionally information about
the minor version. This information is stored in the "analog top"
registers.

Add the nodes for these register blocks so we can decode the SoC type
and version information.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>