ARM: socfpga: Fully unmap the FPGA bridges from L3 space

ARM: socfpga: Fully unmap the FPGA bridges from L3 space

Instead of just putting the bridges into reset, fully remove the bridges
from the L3 main bridge space when disabling them by clearing bits in
NIC-301 remap register. Moreover, only touch the 3 LSbits in brgmodrst
register as the rest of the bits are undefined.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tien Fong Chee <tien.fong.chee@intel.com>