arm64: dts: meson: odroid-c2: Add missing regulator linked to P5V0 regulator

As per schematics VDDIO_AO18, VDDIO_AO3V3/VDD3V3 DDR3_1V5/DDR_VDDC:
fixed regulator output which is supplied by P5V0.

Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>