Rename scteken_revattr() to scteken_sc_to_te_attr(). scteken_revattr()
looked like it might handle reverse attributes, but it actually handles
conversion of attributes in the direction indicated by the new name.
Reverse attributes are just broken.

Rename scteken_attr() to scteken_te_to_sc_attr(). scteken_attr() looked
like it might give teken attributes, but it actually gives sc attributes.

Change scteken_te_to_sc_attr() to return int instead of unsigned int.
u_char would be enough, and it promotes to int, and syscons uses int
or u_short for its attributes everywhere else (u_short holds a shifted
form and it promotes to int too).