agc: support one-word NOP reservations and share packet sizing

src/graphics/guest_gpu/graphicsRun.cpp

@@ -689,7 +689,7 @@ void CommandProcessor::ProcessPm4(Pm4Execution& execution) {
 		const auto        opcode        = (packet_header >> 8u) & 0xffu;
 		EXIT_NOT_IMPLEMENTED(remaining_dw > total_dw);
 
-		if (packet_header == 0x80000000u) {
+		if (packet_header == 0x80000000u || Pm4::PacketSizeDw(packet_header) == 1u) {
 			cursor.offset_dw++;
 			execution.m_made_progress = true;
 			continue;