stm32mp1: pwr: use the last binding for pwr

Update the driver to use the latest binding from kernel v5.5-rc1:
no more use syscon or regmap to access to pwr register and
only one pwr_regulators node with the compatibility "st,stm32mp1,pwr-reg"
is available.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/arch/arm/dts/stm32mp157-u-boot.dtsi b/arch/arm/dts/stm32mp157-u-boot.dtsi
index 0d1d387..cb8d60e 100644
--- a/arch/arm/dts/stm32mp157-u-boot.dtsi
+++ b/arch/arm/dts/stm32mp157-u-boot.dtsi
@@ -128,7 +128,7 @@
 	u-boot,dm-pre-reloc;
 };
 
-&pwr {
+&pwr_regulators {
 	u-boot,dm-pre-reloc;
 };