For incremental build, "include/generated/mach-types.h is up to date"
is every time displayed like follows:

$ make ARCH=arm
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
make[1]: `include/generated/mach-types.h' is up to date.
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h

This commit avoids such a clumsy log and introduces Kbuild standard
log style:

  GEN     include/generated/mach-types.h
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>