clk: samsung: exynos4: Rename exynos4_plls to exynos4x12_plls

This array defines PLLs specific to Exynos 4x12 SoCs and not for all
Exynos 4 SoCs, so the name should represent that.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>