Currently the is_boot_from_usb is checking the USB PHY Powerdown bit. This
way has a defect that if we run any usb function in u-boot the checking will
always return true.
This patch improves the way to avoid such problem above. A new arch-specific flag is
added to indicate if it is USB boot. We check the USB PHY PWD bit at early of boot
stage then set that flag. So any following calling of is_boot_from_usb will return
correct value.
Signed-off-by: Ye Li <ye.li@nxp.com>
0efb6ecdb9