rockchip: clk: rk3368: implement MMC/SD clock reparenting

rockchip: clk: rk3368: implement MMC/SD clock reparenting

The original clock support for MMC/SD cards on the RK3368 suffered
from a tendency to select a divider less-or-equal to the the one
giving the requested clock-rate: this can lead to higher-than-expected
(or rather: higher than supported) clock rates for the MMC/SD
communiction.

This change rewrites the MMC/SD clock generation to:
 * always generate a clock less-than-or-equal to the requested clock
 * support reparenting among the CPLL, GPLL and OSC24M parents to
   generate the highest clock that does not exceed the requested rate

In addition to this, the Linux DTS uses HCLK_MMC/HCLK_SDMMC instead of
SCLK_MMC/SCLK_SDMMC: to match this (and to ensure that clock setup
always works), we adjust the driver appropriately.

This includes the changes from:
 - rockchip: clk: rk3368: convert MMC_PLL_SEL_* definitions to shifted-value form

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>