config: Move the parsing mg-encrypted setting in module-gbox.c

This setting is really obscure and it is a lot of code. Moving the
code in module-gbox.c cleans up oscam-config-reader.c and saves
us nice 1.2k (on x86) binary size savings when gbox module is disabled.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8229 4b0bc96b-bc66-0410-9d44-ebda105a78c1