config-host.mak: rename datadir to qemu_datadir

config-host.mak: rename datadir to qemu_datadir

Autoconf concept of "datadir" is supposed to be "$prefix/share", not
"$prefix/share/PACKAGE", so using datadir for the Qemu-specific
directory is confusing.

The current C code that uses CONFIG_QEMU_DATADIR should be safe, as now
create_config generates the same #define name (CONFIG_QEMU_DATADIR) for
both "datadir" and "qemu_datadir" variables.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>