reset: meson: enable level reset support on Meson8b

Commit a5a10afe ("reset: meson: add level reset support for GX SoC
family") only enabled the level resets for the newer GX SoC family.
However, the older 32-Meson SoCs (Meson8, Meson8b and Meson8m2) also
support level resets using the same offset as the newer GX SoCs.

This removes the separation between Meson8b and the GX SoCs from the
reset-meson driver to enable the level resets also on Meson8b.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>