The PLACEHOLDER was not meant to be used, but c++ doesn't like passing 0
to enums, so it was used. For this reason we add all the NO_FLAGS items,
so the PLACEHOLDER shouldn't be used anymore.
Second, XKB_MAP is the prefix we used ages ago, KEYMAP is the expected
prefix here. So deprecate that as well.
The old names may still be used through the xkbcommon-compat.h header,
which is included by default (no need to include directly).
Signed-off-by: Ran Benita <ran234@gmail.com>