clk: samsung: exynos4: Enable ARMCLK down feature

Enable ARMCLK down feature on all Exynos4 SoCs. The frequency of
ARMCLK will be reduced upon entering idle mode (WFI or WFE).

The feature behaves like very fast cpufreq ondemand governor. In idle
mode this reduces energy consumption on full frequency chosen by
cpufreq governor by approximately:
 - Trats2:  6.5% (153 mA -> 143 mA)
 - Trats:  33.0% (180 mA -> 120 mA)
 - Gear1:  27.0% (180 mA -> 130 mA)

The patch uses simillar settings as Exynos5250 (clk-exynos5250.c),
except it disables clock up feature and on Exynos4412 ARMCLK down is
enabled for all 4 cores.

Tested on Trats board (Exynos4210), Trats2 board (Exynos4412) and
Samsung Gear 1 (Exynos4212).

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>