clk: exynos5250: Update cpufreq related clocks for EXYNOS5250

cpufreq driver for EXYNOS5250 is not a platform driver, hence we cannot
currently pass the clock names through a device tree node. Instead, we
need to make them available through a global alias.

cpufreq driver for EXYNOS5250 requires four clocks - 'armclk',
'mout_cpu', 'mout_mpll' and 'mout_apll'.

'armclk' has already been defined with an alias, 'mout_cpu', 'mout_mpll'
and 'mout_apll' are now defined with an alias.

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>