ARM: EXYNOS: change the name of USB ohci header

This patch changes the name of USB ohci header from 'usb-exynos.h'
to 'usb-ohci-exynos.h'. This is because this header file has
the platdata for only EXYNOS OHCI.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>