mmc: am654_sdhci: Add Support for configuring PHY in J721e

Add Support for writing to PHY registers for J721e. There are number of
differences between the J721e 8 bit PHY, J721e 4 bit PHY and AM654 PHY.
Create a driver_data structure with an ops and flags field and use the
flags field to indicate these differences. The differences are as
follows:

1. The J721e 4 bit instance PHY does not have a DLL. Introduce a
DLL_PRESENT flag to make sure that DLL related registers are accessed
only where they are present. Also add a separate set_ios_post()
callback.

2. The J721e 8 bit instance is not muxed with anything else inside the
SoC and hence the IOMUX_ENABLE filed does not exist. Add a flag which is
used to indicate the presence of this field.

3. The register field used to select DLL frequency is 3 bit wide in
J721e as compared to 2 bits in AM65x. Add another flag that
distinguishes these fields.

4. The strobe select field is 8 bit wide as compared to 4 bit wide for
AM65x. Add yet another flag to indicate this difference. Strobe select
is used only for HS400 speed mode, support for which has not been added
in AM65x.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>