qtuio: correct install-target/staging when Qt library type is 'static'

If BR2_PACKAGE_QT_STATIC is set, qtuio will not build a .so file, but .a.
However, the custom INSTALL_TARGET_CMDS and INSTALL_STAGING_CMDS
unconditionally attempted to copy the .so file.

This commit checks the requested Qt library type and copies the right
library for each case, taking into account that the static .a file does not
need to be copied to the target directory.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>