mtd: rawnand: denali: set SPARE_AREA_SKIP_BYTES based on DT compatible

Currently, the denali NAND driver in U-Boot configures the
SPARE_AREA_SKIP_BYTES based on the CONFIG option.

Recently, Linux kernel merged a patch that associates the proper
value for this register with the DT compatible string.

Do likewise in U-Boot too.

The denali_spl.c still uses CONFIG_NAND_DENALI_SPARE_AREA_SKIP_BYTES.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>