usb: phy: samsung: Pass enable/disable callbacks through driver data

To remove unnecessary if statements, this patch introduces phy_enable
and phy_disable callbacks in driver data structure that implement
SoC-specific PHY initialization and deinitialization.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>