mmc: sdhci-st: Add delay management functions for top registers (eMMC).

mmc: sdhci-st: Add delay management functions for top registers (eMMC).

Due to the tight timing constraints in some UHS modes, it is required to have
some delay management in the design. Two types of delay management are supported
in the HW: -

1) Static delay management
2) Dynamic delay management

NB: The delay management is only there when eMMC interface is selected.

1: Static delay management: is used to provide PVT dependent static delay on the
clock/data lines to manage setup/hold requirements of the interface. The maximum
delay possible is 3.25ns. These delays are PVT dependent, and thus delay values
applied are not accurate and vary across provcess voltage and temperature range.
Due to this these delays must not be used on the very time critical paths.

2. Dynamic delay locked loop (DLL): is used to provide dynamic delay management.
The advantage of DLL is that it provides accurate & PVT indepedent delay.

The DLL is used to provide delay on the loopback clock on "Read Path" to capture
read data reliably. On TX path the clock on which output data is transmitted is
delayed, resulting in delay of TX data.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>