arm/km: skip FPGA config when already configured

arm/km: skip FPGA config when already configured

In order to be able to perform board resets without interrupting the
traffic, the configuration of an already properly configured FPGA is
skipped.

This is because some PCIe FPGAs embed some other function that must
continue to work over reset.

It is then the responsibility of the application to trigger a
reconfiguration when needed. This is done by lowering the FPGA_INIT_B
pin for delaying the configuration to u-boot @ next reboot, and then
lower the FPGA_PROGRAM_B signal.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>