In case USB hub regulator is shared, unexpected behavior occurs.
On stm32mp135f-dk, stm32mp157c-ev1 and stm32mp157x-dkx, regulator
v3v3 is shared between several IP/devices (USB, panel, ethernet phy,
camera, ...).
Running command "usb stop", v3v3 regulator is switched off and
the splashscreen content disappear.

v3v3 shouldn't be disabled on usb_onboard_hub_remove() callback.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Change-Id: If7ed2ccb5a1c1a84637d29d763cc1935d9b8815e
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/u-boot/+/299563
ACI: CITOOLS <MDG-smet-aci-reviews@list.st.com>
Reviewed-by: Fabrice GASNIER <fabrice.gasnier@foss.st.com>
Domain-Review: Fabrice GASNIER <fabrice.gasnier@foss.st.com>