[sma_corr] Added the cgain block arithmetic to the FFT area constraints.

Also, unignored the pblock directory in .gitignore.
[sma_corr] Replaced a Xilinx delay block with a CASPER pipeline in visibs/del.

This should help with meeting timing since this delay was being converted to a
SRL16 and creating large negative slack on that path.
[sma_corr] Set the cgain/gain_[0,1] block memory to use "Low Power".

They are previous set to use "Minimum Area" but this was changed with
the hope that it will help with meeting timing.
[sma_corr] Added area constraints for the visibility network outputs.
[sma_corr] Removed the digital tone and tone+noise in the source blocks.

This is hardly ever used and has been causing serious timing issues.
Revert "[sma_corr] Added area constraints for the visibility network outputs."

This reverts commit 08ec5a0a3bf6ce08a0b2e8587bfe3af1043a4f8d.
[sma_corr] Added pipeline=3 to the path from walsh table to cgain.

This is in an effort to reduce timing errors on these paths.
[cgain_core] Updated; replaced delays with pipelines; increased convert delay by 1.
[cgain_core] Changed the sin/cos lookup to use distributed instead BRAM.