vt(4): Fix a crash in vt_mark_mouse_position_as_dirty() when in textmode

In textmode, no font is loaded, thus the page fault in
vt_mark_mouse_position_as_dirty() when it wants the font width/height.

For now, create a fake area for the textmode. This needs to be modified
if vt_vga gains mouse support in textmode.

While here, fix a build failure when SC_NO_CUTPASTE is defined:
vt_mark_mouse_position_as_dirty() must not be included in this case.

MFC after:	1 week