of/documentation: Update G2D documentation

Exynos5250 G2D IP requires only the gate clock. Update the
binding documentation accordingly.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Inki Dae <inki.dae@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
1 file changed