Is Atmel AT91R4008 supported?

The support list contains AT91, does that mean that AT91R4008 is supported?

That is an ARM7 part, each family of which has a different interrupt controller and different timer to generate the tick interrupt - so to run the code on the part start with a different AT91. If the port you start with has the same timer peripheral as the AT91R4008 then you probably don’t need to do anything. If it doesn’t then you will have to update the prvSetupTimerInterrupt() function in the ports port.c file to use whichever timer is on the AT91R4008 and install the interrupt handler accordingly (the interrupt handler for the tick doesn’t need to change, just the vector it is installed on). I would assume the interrupt controller would be the same across the AT91 families so you probably don’t need to do anything there either - but if the interrupt controller is different you will also need to change the code that configures the interrupt.