qmake5_base.bbclass: Fix mkspec path when building nativesdk binaries

When building nativesdk binaries we ought to rely in the native
mkspecs.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
nativesdk-qttools.inc: Fix installation and packaging

We must to fix the installation paths as did in nativesdk-qtbase.inc
and remove the files unused from the packages. This fixes the
packaging errors and allows for a successful build for SDK.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>