LDPC decoding offload using the XDMA driver

This feature allows to offload LDPC decoding to a FPGA using the XDMA driver in nr_ulsim and nr-softmodem .

Complete coded transport blocks are offloaded through a modification in openair1/PHY/NR_TRANSPORT/nr_ulsch_decoding.c .

This feature is not using any of the existing module interface for LDPC decoding existing in OAI. Instead, third party sources necessary to interface with the XDMA driver was embedded in the PHY_NR static library.

A cleaner integration would rely on a upcoming module interface that allows the decoding implementation to handle complete slots in one call.

Therefore, you may consider merging this branch in order to enable the use of offloading through XDMA as soon as possible at the cost of having the implementation hanging in a static library for a moment. If instead you wish to merge from the beginning a clean implementation as a module, please ignore this MR and expect a rework on the decoding module interface.