soc: amlogic: canvas: add support for Meson8, Meson8b and Meson8m2

The canvas IP on Meson8, Meson8b and Meson8m2 is mostly identical to the
one on GXBB and newer. The only known difference so far is that that the
"endianness" bits are not supported on Meson8m2 and earlier.

Add new compatible strings and a check in meson_canvas_config() to
validate that the endianness bits cannot be configured on the 32-bit
SoCs.

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