msx1: update to new discard
msx2: update to new _discard logic
nc100: update to new _discard
trs80: update to new _discard
pcw8256: update to new _discard
z80pack-lite: update to new _discard
pcw8256: note zero requirement
socz80: update to new _discard
binman: sanity check data area, fix end reporting