Added support for Roland PRO-E Arranger

[giulioz]

Kinda works, timers are flaky, requires external MT-32 emulation (MUNT works). Test mode for RAM and ROM passes.

[happppp]

You forgot to initialize m_baud. If the CPU manual says it's unmodified at reset, do m_baud = 0 at device_start. Also, the new variables each need a save_item.

[giulioz]

@happppp good point, fixed it now

[happppp]

Same thing in the driver by the way: If you want savestates to work, add a save_item to machine_start for keyscan and lcd mode. Also, MAME drivers add m_ prefix to class variables.

[giulioz]

@happppp Should be all done, took note for my future contributions, thanks!

[giulioz]

@angelosa good point, just actioned your feedback. Thanks!