ARM: SAMSUNG: Export MIPI CSIS/DSIM PHY control functions

The s5p_csis_phy_enable/s5p_dsim_phy_enable functions are now used
directly by corresponding drivers and thus need to be exported so
the drivers can be built as modules.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>