dt-bindings: nand: denali: reduce the register space in the example

This example allocates much more than needed for address regions.

As for "denali_reg", as you see in drivers/mtd/nand/denali.h, all
registers fit in 0x1000.

As for "nand_data", this IP is generally configured to use Indexed
Addressing mode, where there are only two registers in the address
translation module (CTRL: 0x00, DATA: 0x10).  Altera SOCFPGA is
also this case.  So, 0x20 is enough.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>