powerpc: remove MBX and MBX860T boards support

Enough time has passed since these boards were moved to Orphan. Remove.

 - Remove board/mbx8xx/*
 - Remove include/configs/{MBX.h,MBX860T.h}
 - Clean-up if defined(CONFIG_MBX)
 - Move the entries 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 7f51991..4e0ad32 100644
--- a/doc/README.scrapyard
+++ b/doc/README.scrapyard
@@ -11,6 +11,7 @@
 
 Board            Arch        CPU            Commit      Removed     Last known maintainer/contact
 =================================================================================================
+mbx8xx           powerpc     mpc8xx         -           2014-04-04
 nx823            powerpc     mpc8xx         -           2014-04-04
 idmr             m68k        mcf52x2        ba650e9b    2014-01-28
 M5271EVB         m68k        mcf52x2        ba650e9b    2014-01-28