mmc: meson-mx-sdio: Refactor internal clock initialization

mmc: meson-mx-sdio: Refactor internal clock initialization

Use modern common clock framework helpers for simplifying the clock
controller management:
- switch to struct clk_hw for internal clocks and only get the
  "cfg_div_clk" (which has to be managed at runtime) as struct clk
  using devm_clk_hw_get_clk() which is then the only clock used by
  struct meson_mx_mmc_host.
- use CLK_HW_INIT_FW_NAME and CLK_HW_INIT_HW helper macros for simpler
  init data initialization
- keep the clock controller memory allocation separate to prevent a
  potential use-after-free because struct meson_mx_mmc_host_clkc is
  free'd before controller_dev

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>