First of 3 banks promoted from async reg array to an sd_bram. Read port
muxed by phase (ST_M load drives pm_a_full, else dbg index); sd_bram's
internal rd_addr_r replaces the explicit pm_a_rd reg (identical 1-cyc
latency). Write port driven combinationally so the posedge write matches the
old nonblocking reg-array timing. 11/11 KAT PASS, byte-exact.