nand_spl: remove P1023RDS_NAND support

Commit 3d5a335c announced that all the nand_spl boards
would be removed before v2014.07 release.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Series-to: uboot
Series-cc: trini
Series-cc: wd
Cover-letter:
Remove all the remaining nand_spl boards

There are still 7 nand_spl boards.

I built all the other boards and
confirmed this series has no impact on them.

END
nand_spl: remove MPC8572DS_NAND support

Commit 3d5a335c announced that all the nand_spl boards
would be removed before v2014.07 release.
nand_spl: remove MPC8569MDS_NAND support

Commit 3d5a335c announced that all the nand_spl boards
would be removed before v2014.07 release.
nand_spl: remove MPC8536DS support

Commit 3d5a335c announced that all the nand_spl boards
would be removed before v2014.07 release.
nand_spl: remove MPC8315ERDB_NAND support

Commit 3d5a335c announced that all the nand_spl boards
would be removed before v2014.07 release.
nand_spl: remove simpc8313 support

Commit 3d5a335c announced that all the nand_spl boards
would be removed before v2014.07 release.

Also update README.scrapyard.
nand_spl: remove nand_spl infrastructure

Remove the common infrastructure of nand_spl and
clean-up the code inside ifdef(CONFIG_NAND_U_BOOT)..endif.