I have given a look at this the last night and for me the problem is not in the driver. At the line 268 of devcpu.c. the CPU registers is added in the m_state_list, only if they have a name and the LR35902_SPEED has not name defined in CPU_GET_INFO. A quick fix is add tihs line in the CPU_GET_INFO

case CPUINFO_STR_REGISTER + LR35902_SPEED: sprintf(info->s, "SPEED:%02X", 0x7E | ( ( cpustate->w.gb_speed - 1 ) << 7 ) | cpustate->w.gb_speed_change_pending); break;

but maybe can be fixed in other way