stm32mp1: disable USB phy supply in sp_min

PMIC ldo4 (vdd_usb 3v3) regulator is enabled in PMIC NVM for boot from USB.
This regulator is used by the USB HS phy.
There is a requirement in AN5031 [1] regarding this regulator:
"VDD3V3_USBHS must not be present unless VDDA1V8_REG is present, otherwise
permanent STM32MP15x lines damage could occur. Must be ensured by PMIC
ranking order or with external component in case of discrete component
power supply implementation".
VDD3V3_USBHS is PMIC vdd_usb regulator, provided by LDO4.
VDDA1V8_REG is PWR reg18 regulator.
It means that vdd_usb must not be ON unless reg18 is ON.
To follow this requirement and ensure vdd_usb will not be ON while reg18
OFF, disable ldo4 regulator.

[1] https://www.st.com/resource/en/application_note/dm00389996-getting-started-with-stm32mp151-stm32mp153-and-stm32mp157-line-hardware-development-stmicroelectronics.pdf



Change-Id: I31adcba720cdee8f2737635821c2273c4835edfb
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/192905


Reviewed-by: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Reviewed-by: CIBUILD <MDG-smet-aci-builds@list.st.com>
Reviewed-by: Lionel DEBIEVE <lionel.debieve@foss.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@foss.st.com>