usb:hsotg:samsung: Use of regulator_bulk_* functions for USB regulators

usb:hsotg:samsung: Use of regulator_bulk_* functions for USB regulators

This commit adds support for supply voltage management for s3c-hsotg IP
block. For that purpose a convenient regulator_bulk_* functions have been
used.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Liam Girdwood <lrg@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>