board: cssi: Read and display MCR board address

MCR boards are plugged in racks. The position in the rack can be read
in a register.

For MCR3000, that's provided by the FPGA so check it is loaded before
reading the address.

For the other boards, the FPGA is loaded by hardware so it can be
read inconditionnaly.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>