ARM: dts: socfpga: arria10: Increase boot partition size for NAND

Increase boot partition size to 32MB to support bigger size kernel image
and FPGA bitstream.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>