ARM: dts: stm32: Repair PMIC configuration on AV96

The vdd PMIC buck regulator was misconfigured, which caused instability
of the board and malfunction of high-speed interfaces, like the RGMII.
Configure the PMIC correctly to repair these problems. Also add missing
Enpirion regulator for the IO voltage into the DT.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>