FLX-2533 strips DCS data path

Code for identifying and copying register reads to a separate axis FIFO functional. Reverted DecEgroup_8b10b_tb.vhd to pre strips-extras version, adding compatibility mods only. Added Strips specific TB (as DecEgroup_8b10b_Strips_tb.vhd) to allow DUT instantiation with generics set as per strips. To evaluate to total resource usage, 2 other branches have been merged into to this one too:

• FLX-2455_reopened_update_direct_mode : Add direct-mode functionality to encoder - increases utilisation
• phase2/FLX-2620_merge_R3L1_cmd_conf_into_LCB : Simplification downlink/encoder by merging/simplifying/removing R3L1 logic into LCB blocks to reduce resource utilisation

Closes FLX-2533