USB: s3c-hsotg: add support for clock gating

This patch adds support for clock gating of the HS/OTG block. On S5PV210
otg gating clock is initally disabled so the driver needs to get and
enable it before it can access its registers.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>