ARM: davinci: add back dummy header files

The mach/dm365.h and mach/dm646xh headers are currently being included
in some device drivers. The removal of those includes is already merged
in some subsystem trees, but adding the dummy files ensures that this
branch can be built standalone.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>

arch/arm/mach-davinci/include/mach/dm365.h

+/* empty, remove once unused */

arch/arm/mach-davinci/include/mach/dm646x.h

+/* empty, remove once unused */