Make the keyboard layer Unicode aware.

Just take keyent_t to use an u_int to store the Unicode codepoints.
Unfortunately the keymap is now too big to be loaded using an ioctl
argument, so change the ioctl to pick a pointer.

This change breaks kbdcontrol ABI. It doesn't break X11, because X11
doesn't do anything with syscons keymaps. It just switches the device
out of K_XLATE.

Obtained from: //depot/user/ed/newcons/...