usb: musb: mediatek: Expose role-switch control to userspace

The allow_userspace_control flag enables manual role-switch from userspace.
Turn this feature on like several other USB DRD controller drivers.

Tested-by: Frank Wunderlich <frank-w@public-files.de>
Acked-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Sungbo Eo <mans0n@gorani.run>
Link: https://lore.kernel.org/r/20210830155903.13907-3-mans0n@gorani.run


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>