When u-boot boots the board may be powering vbus, we turn off vbus in
sunxi_usbc_request_resources, if we are too quick with reading vusb-detect
after this we may see a residual charge and assume we've an external vusb
connected even though we do not. So when we see an external vusb wait a bit
and try again.

Without this when dealing with a pmic controller vbus and doing "reset" on
the u-boot console the musb host will only init once every other boot, because
the other boot it thinks an external vbus is present, this commit fixes this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>