configs: iocon: Enabling CONFIG_CMD_FPGAD again

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Revert changes in iocon.h config file caused by
these two commits:
"configs: iocom: Fix typo on CMD_FPGA command"
(sha1: d0db28f9)
and
"fpga: Guard the LOADMK functionality with CMD_FPGA_LOADMK"
(sha1: 64e809af)

CONFIG_CMD_FPGAD is own command.

Reported-by: Dirk Eibach <dirk.eibach@gdsys.cc>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>