kconfig qconf: add namespace for use of Key_ enum values

They are defined in the 'Qt' namespace.

Fixes the following compiler errors after a quick conversion with 'qt3to4',
which occured with g++ 3.4.6 and 4.1.2, but not anymore with 4.3.2.

scripts/kconfig/qconf.cc: In member function 'virtual void ConfigLineEdit::keyPressEvent(QKeyEvent*)':
scripts/kconfig/qconf.cc:311: error: 'Key_Escape' was not declared in this scope
scripts/kconfig/qconf.cc:313: error: 'Key_Return' was not declared in this scope
scripts/kconfig/qconf.cc:314: error: 'Key_Enter' was not declared in this scope

scripts/kconfig/qconf.cc: In member function 'virtual void ConfigList::keyPressEvent(QKeyEvent*)':
scripts/kconfig/qconf.cc:653: error: 'Key_Escape' was not declared in this scope
scripts/kconfig/qconf.cc:666: error: 'Key_Return' was not declared in this scope
scripts/kconfig/qconf.cc:667: error: 'Key_Enter' was not declared in this scope
scripts/kconfig/qconf.cc:681: error: 'Key_Space' was not declared in this scope
scripts/kconfig/qconf.cc:684: error: 'Key_N' was not declared in this scope
scripts/kconfig/qconf.cc:687: error: 'Key_M' was not declared in this scope
scripts/kconfig/qconf.cc:690: error: 'Key_Y' was not declared in this scope

scripts/kconfig/qconf.cc: In constructor 'ConfigMainWindow::ConfigMainWindow()':
scripts/kconfig/qconf.cc:1329: error: 'CTRL' was not declared in this scope
scripts/kconfig/qconf.cc:1329: error: 'Key_Q' was not declared in this scope
scripts/kconfig/qconf.cc:1331: error: 'Key_L' was not declared in this scope
scripts/kconfig/qconf.cc:1333: error: 'Key_S' was not declared in this scope
scripts/kconfig/qconf.cc:1340: error: 'Key_F' was not declared in this scope

Signed-off-by: Markus Heidelberg <markus.heidelberg@web.de>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>