[media] s5p-csis: Replace phy_enable platform data callback with direct call

The phy_enable callback is common for all Samsung SoC platforms,
replace it with direct function call so the MIPI-CSI2 DPHY control
is also possible on device tree instantiated platforms.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>