Toshiba T3100e improvements :

* Enables [Fn]+key combinations (using right-Ctrl or right-Alt as [Fn]). In particular:
* Implements switching the built-in display adapter between the 'internal' plasma display ([Fn]+[Home]) and an 'external' CGA monitor ([Fn]+[End])
* Allows the video font to be toggled between thin and thick ([Fn]+[Right arrow]).
* Implements the four hardware fonts of the original, selectable in BIOS setup.
* Implements CRTC register 12h (attribute mapping and display type)
Patch from John Elliott

src/vid_t3100e.h

@@ -1,3 +1,4 @@
 extern device_t t3100e_device;
 
 void t3100e_video_options_set(uint8_t options);
+void t3100e_display_set(uint8_t internal);