clk: samsung: exynos5420: Add SET_RATE_PARENT flag to clocks on G3D path

Add CLK_SET_RATE_PARENT flag to all clocks on the path from VPLL to G3D,
so the G3D MALI driver can simply adjust the rate of its clock by doing
a single clk_set_rate() call, without the need to know the whole clock
topology in Exynos542x SoCs.

Suggested-by: Marian Mihailescu <mihailescu2m@gmail.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>