clk: samsung: exynos3250: Enable ARMCLK down feature

Enable ARMCLK down feature on Exynos3250 SoC. The frequency of
ARMCLK will be reduced upon entering idle mode (WFI or WFE).

The feature behaves like very fast cpufreq ondemand governor.

The patch uses simillar settings as Exynos5250 (clk-exynos5250.c),
except it disables clock up feature.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Tomasz Figa <t.figa@samsung.com>