powerpc: remove NX823 board support

Enough time has passed since this board was moved to Orphan. Remove.

 - Remove board/nx823/*
 - Remove include/configs/NX823.h
 - Clean-up ifdef(CONFIG_NX823)
 - Move the entry from boards.cfg to doc/README.scrapyard

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/doc/README.scrapyard b/doc/README.scrapyard
index 0a6c6b5..7f51991 100644
--- a/doc/README.scrapyard
+++ b/doc/README.scrapyard
@@ -11,8 +11,9 @@
 
 Board            Arch        CPU            Commit      Removed     Last known maintainer/contact
 =================================================================================================
-idmr             m68k        mcf52x2        -           2014-01-28
-M5271EVB         m68k        mcf52x2        -           2014-01-28
+nx823            powerpc     mpc8xx         -           2014-04-04
+idmr             m68k        mcf52x2        ba650e9b    2014-01-28
+M5271EVB         m68k        mcf52x2        ba650e9b    2014-01-28
 dvl_host         arm         ixp            e317de6b    2014-01-28  Michael Schwingen <michael@schwingen.org>
 actux4           arm         ixp            6ff7aafa    2014-01-28  Michael Schwingen <michael@schwingen.org>
 actux3           arm         ixp            38da33f3    2014-01-28  Michael Schwingen <michael@schwingen.org>