board: cssi: Load FPGA on MCR3000 board

Unlike CMPC885 and CMPCPRO boards, the FPGA of MCR3000 board doesn't
load code automatically but needs to be loaded by software through SPI.

Until now it was loaded later by Linux, but we'd like U-boot to have
access to some information that require the FPGA, like board address
in racks.

So, implemented the load of FPGA in U-boot.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
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To avoid spamming your email boxes, the code isn't included in
the emailed patch but will be present in the PULL request