sunxi: musb: Support checking VBUS using AXP221 PMIC

sunxi: musb: Support checking VBUS using AXP221 PMIC

This enables the musb glue layer to use the AXP221's VBUS detection
function to check for VBUS. This fixes otg support on the A23 q8h
tablets.

Note that u-boot never calls musb_shutdown(), so once VBUS is enabled,
it is never disabled until the system is powered off, or the OS does
so. This can be used to our advantage to keep VBUS powered into the
OS, where support for AXP221 is not available yet.

Fixes: 52defe8f6570 ("sunxi: musb: Check Vbus-det before enabling otg port power")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>