arm: socfpga: soc64: Check FPGA Config status register before bridge reset

Instead of querying SDM for FPGA configuration status through mailbox
messages, U-Boot now checks System Manager's FPGA Config status register
for FPGA configuration status before resetting bridge.

Signed-off-by: Chee Hong Ang <chee.hong.ang@intel.com>
Reviewed-by: Ley Foon Tan <ley.foon.tan@intel.com>