usb: gadget: s3c-hsotg: add proper suspend/resume support

This patch adds suspend/resume support to s3c-hsotg driver. It makes UDC
driver more power efficient.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>