hdl/ip_cores/dsp-cores: update submodule reference
hdl/modules/pcie/*/Manifest.py: removed unexisting module

 - Removed unexisting module from Manifest files.
 	It was referenced here by error.
hdl/testbench/*/wb_acq_core_test/*: add instructions on README

There is an error when simulating the RS232 module with
modelsim. For now, it is safe to exclude the file from the
Manifest file (see README), as we do not use it in simulation.