If kernel/config.h is included in yportenv.h, then yportenv.h must be

If kernel/config.h is included in yportenv.h, then yportenv.h must be
always included.  Move it outside of ifdef CONFIG_YAFFS_MTD_ENABLED.

added in additional configuration conditionals to shut up gcc about
defined but not used functions in yaffs_fs.c

added in NOTYET around functions that aren't currently used in
yaffs_tagscompat.c to shut up gcc about defined but not used function.