kconfig: qconf: create QApplication after option checks

'scripts/kconfig/qconf -h' just calls usage() and exits, with
QApplication unused.

There is no need to construct QApplication so early. Do it after
the parse stage.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>