memory: move jedec_ddr.h from include/memory to drivers/memory/

Now that jedec_ddr_data.c was moved from lib/ to drivers/memory/,
<memory/jedec_ddr.h> is included only from drivers/memory/.

Make it a local header of drivers/memory/.

The directory include/memory is now gone.

While I am here, I also changed #include <linux/module.h> to
<linux/export.h>. Because CONFIG_DDR is bool, jedec_ddr_data.c is
never compiled as a module.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Olof Johansson <olof@lixom.net>