ARM: dts: stm32mp157c-ed1: Add regulator node

Add regulator nodes needed by stpmu1 regulator driver
Add vmmc-supply and vqmmc-supply regulator property for
sdmmc1 and sdmmc2.

Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>