usb: hsotg: samsung: Replace endpoint specific locks with a global lock

The endpoint specific locks are replaced with a global lock.
This is crucial for running s3c-hsotg driver on a SMP SoC.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>