support multiple slots per partition

[amamory]

FRED runtime supports multiple slots per partitions. However, DART doesnt.
Multiple slots per partition would give to a certain IP multiple reconfigurable regions to be used in runtime.
It means that the FRED scheduler could choose where (i.e. which reconfigurable region) to deploy a certain IP.

Note that, in pr_tool::generate_fred_files, in the part that writes the arch.csv file, the slot information is fixed to 1 since dart only supports 1 slot per partition..