Keep real and virtual mods in the same table in the keymap

Keep real and virtual mods in the same table in the keymap

We change the keymap->vmods array into keymap->mods, and change it's
member type from struct xkb_vmod to struct xkb_mod. This table now
includes the real modifiers in the first 8 places. To distinguish
between them, we add an enum mod_type to struct xkb_mod.

Besides being a more reasonable approach, this enables us to share
some code later, remove XKB_NUM_CORE_MODS (though the 0xff mask still
appears in a few places), and prepares us to flat out remove the
distinction in the future. This commit just does the conversion.

Signed-off-by: Ran Benita <ran234@gmail.com>