Update vivado version to 2020.2:
- update default vivado version from 2020.1 to 2020.2
- add conditions to apply specific contraints only in Out Of Context mode.
- update DDR controler parameters for vcu118 and kcu105 dev boards
The new REG_PRBS_CNTRL and REG_PRBS_STATUS registers expose controls of internal
PRBS generators and checkers allowing the testing the multi-gigabit serial link
at the physical layer without the need of the link layer bringup.
Xilinx recommends that all synchronizer flip-flops have
their ASYNC_REG property set to true in order to preserve the
synchronizer cells through any logic optimization during synthesis
and implementation.