mmc: exynos_dw_mmc: Obtain and use CIU clock via CCF API

mmc: exynos_dw_mmc: Obtain and use CIU clock via CCF API

New Exynos chips should implement clock drivers using CCF framework. In
that case corresponding CCF functions can be used to get/set the clock
rates. Moreover, already existing get_mmc_clk() and set_mmc_clk() calls
are only implemented for CONFIG_CPU_V7A (i.e. ARM32 chips). In case of
ARM64 chips that config option is not defined, so build will crash on
linking stage, with errors like these:

    ld: drivers/mmc/exynos_dw_mmc.o:
      in function `exynos_dwmci_get_sclk':
      undefined reference to `get_mmc_clk'
    ld: drivers/mmc/exynos_dw_mmc.o:
      in function `exynos_dwmci_set_sclk':
      undefined reference to `set_mmc_clk'

Fix that issue by using CCF clocks API on ARM64 platforms for getting
and setting the source clock (sclk = SDCLKIN = CIU) rate. To implement
this, first extract the existing ARM32 clock control code into helper
functions with more generic signatures to abstract getting/setting the
sclk rate. Then add CCF clock support to those functions for ARM64
platforms.

Fixes: a082a2dde061 ("EXYNOS5: DWMMC: Added FDT support for DWMMC")
Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>