refactor(stm32mp1): remove the support of calibration result

The support of a predefined DDR PHY tuning result is removed for
STM32MP1 driver because it is not needed at the supported frequency
when built-in calibration is executed.

The calibration parameters were provided in the device tree by the
optional node "st,phy-cal", activated in ddr helper file by the
compilation flag DDR_PHY_CAL_SKIP and filled with values generated
by CubeMX.

This patch
- updates the binding file to remove "st,phy-cal" support
- updates the device trees and remove the associated defines
- simplifies the STM32MP1 DDR driver and remove the support of
  the optional "st,phy-cal"

After this patch the built-in calibration is always executed.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>
Change-Id: I3fc445520c259f7f05730aefc25e64b328bf7159