Bluetooth: Mesh: Check that required models exists on the same element

Referring to MshDFU_v1.0 Sections 6.1.1, 6.2.1 and  7.1.1 model
descriptions: DFU/DFD server/clients extend BLOB Transfer root models
and DFD server requires Firmware Update Client on the same element. For
this reason we need to make sure that those main models or root models
exist on the same element. And also firmware update client can not be
forced to be in the first element.

For all model extention call return the error code in case of an error.

Signed-off-by: alperen sener <alperen.sener@nordicsemi.no>