When booting from USB, the bootrom sets the VUSB_IN_PMID bit of the MISC2
register of the TWL6030. However, U-Boot sets the VUSB_IN_VSYS bit to enable
VBUS input. As both bits are contradictory, enabling both disables the input,
according to the TWL6030 TRM.

Thus, we need to clear the VUSB_IN_PMID bit in case of an USB boot (which could
just as well be a memory boot after USB timed out).

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>