cups: Enable serial backend
cups: Enable serial backend

    Enable building the backend for serial printers.

Signed-off-by: Florian Boor <039f13934429c3e687fd452ce64217cbd7f1565d@kernelconcepts.de>

giobauermeister/openembedded,JamesAng/oe,xifengchuo/openembedded,hulifox008/openembedded,openembedded/openembedded,giobauermeister/openembedded,xifengchuo/openembedded,xifengchuo/openembedded,hulifox008/openembedded,hulifox008/openembedded,hulifox008/openembedded,hulifox008/openembedded,JamesAng/oe,xifengchuo/openembedded,JamesAng/oe,giobauermeister/openembedded,JamesAng/oe,openembedded/openembedded,openembedded/openembedded,openembedded/openembedded,openembedded/openembedded,xifengchuo/openembedded,JamesAng/oe,openembedded/openembedded,xifengchuo/openembedded,openembedded/openembedded,openembedded/openembedded,giobauermeister/openembedded,xifengchuo/openembedded,hulifox008/openembedded,openembedded/openembedded,giobauermeister/openembedded,xifengchuo/openembedded,openembedded/openembedded,xifengchuo/openembedded,JamesAng/oe,giobauermeister/openembedded,hulifox008/openembedded,giobauermeister/openembedded,giobauermeister/openembedded,openembedded/openembedded,giobauermeister/openembedded,JamesAng/oe