soc: amlogic: meson-gx-pwrc-vpu: Fix power on/off register bitmask

The register bitmask to power on/off the VPU memories was incorectly set
to 0x2 instead of 0x3. While still working, let's use the recommended
vendor value instead.

Fixes: 75fcb5ca ("soc: amlogic: add Meson GX VPU Domains driver")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>