package/kodi-platform: new package

This package is used by the PVR addon packages and has no use by itself,
therefore is does not show up in menuconfig.

[Thomas:
 - fix license information, as noticed by Yann E. Morin: the license
   is GPLv2+, not GPLv3+, and there is no COPYING file, so a short
   source file with the license header was used instead.
 - remove -DCMAKE_MODULE_PATH, no longer needed now that
   kodi-config.cmake is fixed.
 - add patch to fix kodi-platform-config.cmake for cross-compilation.]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>