qt4-tools-nativesdk: improve and tidy up qmake build

qt4-tools-nativesdk: improve and tidy up qmake build

* Use the same method to build qmake as in the qt4 target recipes
* We always have qmake from qt4-native so don't check if it exists -
  just skip the check like we do in the qt4 target recipes. This
  saves us a patch.
* Replace qt4-tools-native in DEPENDS with qt4-native

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>