phy: phy-samsung-usb2: Change phy power on/power off sequence

The Exynos4412 USB 2.0 PHY hardware differs from the description provided
in the documentation. Some register bits have different function. This
patch fixes the defines of register bits and changes the way how phys are
powered on and off.

Signed-off-by: Kamil Debski <k.debski@samsung.com>
Tested-by: Daniel Drake <drake@endlessm.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>