usb: gadget: s3c-hsudc: move platform_data struct to global header

Gadget drivers should be compilable on all architectures.
This patch removes one dependency on architecture-specific code.

Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>