The raspi MATLAB interface requires a server running on the Raspberry Pi hardware. This is a custom server that interprets commands send by MATLAB. If you just install the Raspbian image provided by the foundation, you won't have this server on your Linux distribution. By the way the Raspbian image downloaded by the targetupdater uses the Raspbian image provided by the http://www.raspberrypi.org/downloads. It just has some extra Linux packages and the server for raspi interface to provide compatibility with MATLAB/Simulink.
In any case, if you still want to use the Raspbian image provided by foundation you may try MATLAB functions shipped in the R2015a support package to add the server to your existing Raspbian image:
raspi.internal.firmware.setupMATLABServer('<IP address>','<User name>','<Password>')
raspi.internal.firmware.setupMATLABDaemon('<IP address>','<User name>','<Password>')
The first function adds the server and the second sets up a daemon so that the server auto-starts at boot. Note that these are unsupported functions. In case of error you need to diagnose the issue on your own. We use these functions to generate the firmware image the targetupdater downloads.
Note: Enabling Device Tree (DT) in the 3.18+ kernels result in some peripherals to not work properly (I2C, SPI). I would recommend disabling DT in the raspi-config utility when using your own image.
