meson: fix dependency on qemu-keymap

meson: fix dependency on qemu-keymap

When qemu-keymap is not available on the host, and enable-xkbcommon
is specified, parallel make fails with:

  % make clean
  ...
  % make -j 32
  ...
  FAILED: pc-bios/keymaps/is
  ./qemu-keymap -f pc-bios/keymaps/is -l is
  /bin/sh: ./qemu-keymap: No such file or directory
  ... many similar messages ...

The code always runs find_program, rather than waiting to build
qemu-keymap, because it looks for CONFIG_XKBCOMMON in config_host
rather than config_host_data.  Making serially succeeds, by soft
linking files from pc-bios/keymaps, but that is not the desired
result for enable-xkbcommon.

Examining all occurrences of 'in config_host' for similar bugs shows one
instance in the docs, which is also fixed here.

Fixes: 4113f4cfee ("meson: move xkbcommon to meson")

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1675708442-74966-1-git-send-email-steven.sistare@oracle.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>