hw: Mask TCDM write data stability check on reads

[paulsc96]

pulp-platform/common_cells#200, recently included by a dependency update, may trigger false-positive TCDM stability assertion errors in some cases when using SSRs.

This is because SSR write data is hardwired to the bidirectional data FIFO output. Therefore, on reads, the write data bits may change irrespective of when a read request is pending. This instability is benign, but causes the payload-wide assertion to fail.

This PR, together with pulp-platform/common_cells#219, fixes this issue by masking stability assertion on the write data and mask inside stream_xbar and stream_omega_net and then conditionally asserting write data and mask stability on reads and atomics in snitch_tcdm_interconnect.

A more general discussion is maybe in order on whether SSRs should invest additional logic to instead mask write data on reads, but we should first fix the bug and then ponder design improvements.

TODO:

• Merge stream-xbar: Add payload stability assertion mask common_cells#219, get common_cells release.
• Update common_cells dependency.
• Before merge, re-verify this banishes assertion misfires in e.g. sw: Add SARIS kernels #124.

[colluca]

LGTM :)