usb: mtu3: move vbus and mode debugfs interfaces into mtu3_debugfs.c

Due to the separated debugfs files are added, move vbus and mode
debugfs interfaces related with dual-role switch from mtu3_dr.c
into mtu3_debugfs.c

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>