[U-Boot] changing of fastboot index

[Sam Protsenko]

Hi Jean-Jacques,

After commit aec0081093e7 ("configs: am57xx_evm: Enable DM_USB and
DM_USB_DEV") I noticed that "fastboot 1" command doesn't work anymore
on BeagleBoard X15. Instead, "fastboot 0" works.

I can see that this happens because in dwc3_glue_bind() we only
register usb at 488d0000 as OTG controller ("dwc3-generic-peripheral"),
and usb at 48890000 is registered as HOST controller ("xhci-dwc3"). This
leads for dwc3_glue_probe() to be only called once (for OTG
controller), so now we only have registered controller with index = 0,
when we are calling usb_gadget_initialize() from do_fastboot_usb().

The reason why I'm bringing this up is that we still have
CONFIG_FASTBOOT_USB_DEV=1 for AM57x-based boards, and "fastboot
reboot-bootloader" won't work, and all documentation needs to be
changed.

In "help fastboot" output it only says that <controller> must be
passed. Do we actually understand which controller is referred here?
Frankly, I never thought about this before. Is it OTG controller
number, or USB controller number? As I understand it, it should be USB
controller index, so on X15 it actually should be "fastboot 1". But I
can be mistaken :) Is this an intended behavior or should we fix it?
If so, can you please help me here?

Thanks!