Update ppc64le config files: disable STE_MODEM_RPROC
    
    Disable config option STE_MODEM_RPROC on all ppc64le flavors, because
    it draws dependencies which aren't available on ppc64le:
    
    warning: (REMOTEPROC && RPMSG) selects VIRTUALIZATION which has unmet direct dependencies (!CPU_LITTLE_ENDIAN)