kconfig: qconf: compile moc object separately

Currently, qconf.moc is included from qconf.cc but they can be compiled
independently.

When you modify qconf.cc, qconf.moc does not need recompiling.

Rename qconf.moc to qconf-moc.cc, and split it out as an independent
compilation unit.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>