usb: dwc2: gadget: fix calls to phy control functions in suspend/resume code

This patch moves calls to phy enable/disable out of spinlock protected
blocks in device suspend/resume to fix incorrect caller context. Phy
related functions must not be called from atomic context. To protect
device internal state from a race during suspend, a call to
s3c_hsotg_core_disconnect() is added under a spinlock, what prevents any
further activity on the usb bus.

Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>