Add sleep related assertion

[Silabs-ArjanB]

We need an assertion (on the free running clock) checking the following:

If core_sleep_o = 1, then the following should be 0:

instr_req_o data_req_o fencei_flush_req_o compressed_valid issue_valid commit_valid mem_ready mem_result_valid result_ready debug_havereset_o, debug_halted_o

and the following should be 1:

debug_running_o

and the following should hold:

(write buffer) state ==WBUF_EMPTY // Write buffer should be empty (load store unit) cnt_q == 0 // There should be no outstanding transactions (lsu response filter) bus_cnt_q == 0 // No core side outstanding transactions (lsu response filter) core_cnt_q == 0 // No core side outstanding transactions