Convert CONFIG_SYS_NAND_MAX_OOBFREE et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_NAND_MAX_OOBFREE
   CONFIG_SYS_NAND_MAX_ECCPOS

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>