Summary

Change the "Enabled" option for the IRQ of on-board RTCs of Multitech PC-500 (plus) and Thomson TO16 to "IRQ 2" to be clearer; get rid of the superfluous "RTC IRQ 2" string.

Drive-bys:

• Fix two incorrect source strings in 86box.pot;
• Move the newly added externs of on-board RTC device_ts from m_xt.c to isartc.h.

Checklist

• Closes #xxx
• I have tested my changes locally and validated that the functionality works as intended
• I have discussed this with core contributors already
• This pull request requires changes to the ROM set
  • I have opened a roms pull request - https://github.com/86Box/roms/pull/changeme/

References

N/A