ARM: dts: stm32: add power supply of otm8009a on stm32mp157c-dk2

This patch adds a new property (power-supply) to panel otm8009a (orisetech)
on stm32mp157c-dk2  & regulator v3v3.

Signed-off-by: Yannick Fertré <yannick.fertre@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>