Fix stlport includes in makefiles

BZ: 207083

According to libstlport.mk, to use stlport for a given target, we shall
"include external/stlport/libstlport.mk" in the target.
This was not done in the parameter-framework's makefiles.

This patch change all targets which require stlport to include it in the
correct way.

Change-Id: Ie9b75af6269f172ad6a6c753e15efd0c7baafdd9
Signed-off-by: Mattijs Korpershoek <mattijsx.korpershoek@intel.com>