cpufreq: exynos: remove dead ->need_apll_change method

cpufreq: exynos: remove dead ->need_apll_change method

Commit 26ab1c62b6e1 ("cpufreq: exynos5250: Set APLL rate
using CCF API") removed the last user of ->need_apll_change
method.  Remove it and then cleanup exynos_cpufreq_scale()
accordingly.

This patch was tested on Exynos4412 SoC based Trats2 board.

There should be no functional changes caused by this patch.

Cc: Sachin Kamat <sachin.kamat@linaro.org>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Kukjin Kim <kgene@kernel.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>