mmc: am654_sdhci: Add flag for PHY calibration

Not all controllers need calibration for the PHY DLL. Add a DLL_CALIB
flag to indicate the same.

Also move the write of trm_icp and driver strength to the set_clock()
function to match the kernel configuration flow.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>