board: stm32mp1: fixup the usb product id for USB download gadget

Select the correct USB product id used by the download gadget
for ST stm32mp1 boards.

The board stm32mp1 select the correct product id, as defined in
http://www.linux-usb.org/usb.ids

 for the STMicroelectronics
vendor id = 0x0483 (CONFIG_USB_GADGET_VENDOR_NUM):
- dfu = 0xdf11 : STM Device in DFU mode
  it is the value used by ROM code and reused for stm32prog
  command
- fasboot = 0x0afb : Android Fastboot device
- others = 0x5720 (CONFIG_USB_GADGET_PRODUCT_NUM)
  Mass Storage Device
  it is used for UMS command / usb_dnl_ums

This patch avoid conflict when the same USB VID/PID is used for
ums, fastboot or dfu command (two different protocols associated
to the same PID).

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>