Added warning during registration of a yet unknown skinny devicetype. Extended the sccp_enum_macro to allow check existence of a enum entry. Added SKINNY_DEVICETYPE_NOTDEFINED as last entry to prevent having to sort these enum entries

git-svn-id: https://svn.code.sf.net/p/chan-sccp-b/code/trunk@5470 43c1dc8c-776e-4df2-8ef1-6e829299be21