Convert rest of names in xkb_keymap back to atoms

Convert rest of names in xkb_keymap back to atoms

These were kept as atoms, but since the keymap was exposed in the API,
we converted them to strings; no the keymap is no longer exposed, so we
can go back to atoms. They make the keymap smaller (at least on 64-bit
machines) and the comparisons faster.

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