powerpc/t4qds: Move doc/README.t4240qds under board/freescale/t4qds

Board specific README file should be moved to board folder.

Signed-off-by: York Sun <yorksun@freescale.com>
diff --git a/doc/README.t4240qds b/board/freescale/t4qds/README
similarity index 100%
rename from doc/README.t4240qds
rename to board/freescale/t4qds/README