fix the following 'make includecheck' warning:

  arch/arm/mach-davinci/board-dm646x-evm.c: mach/common.h is included more than once.
Signed-off-by: NJaswinder Singh Rajput <jaswinderrajput@gmail.com>
Acked-by: NKevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>