usb: musb: Add get/set toggle hooks

usb: musb: Add get/set toggle hooks

Add get/set toggle hooks in struct musb_io and struct musb_platform_ops
for special platform; remove function musb_save_toggle, use the set/get
callback to handle toggle.

Signed-off-by: Min Guo <min.guo@mediatek.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Link: https://lore.kernel.org/r/20200115132547.364-21-b-liu@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>