ti: keystone: Clean up or migrate some NAND related options.

ti: keystone: Clean up or migrate some NAND related options.

The COFNIG_KEYSTONE_RBL_NAND option is always enabled for the driver on
keystone platforms, but not older davinci platforms.  Use def_bool for
the symbol. For CONFIG_KEYSTONE_NAND_MAX_RBL_PAGE, it's only used within
the driver and derived from another symbol, so remove CONFIG from the
name.  Finally, CONFIG_KEYSTONE_NAND_MAX_RBL_SIZE is a bit more fixed.
For now, use the value directly.  Long term, as part of DM'ifying NAND,
this should come from the device tree.

Signed-off-by: Tom Rini <trini@konsulko.com>