ARM: 8576/1: avoid duplicating "Kernel: arch/arm/boot/*Image is ready"

Commit 3939f334

 ("ARM: 8418/1: add boot image dependencies to
not generate invalid images") fixed bad image generation for the
parallel building, but as its side effect, Kbuild now descends into
arch/arm/boot/ again and again, duplicating the log messages.
It looks clumsy, so let's display the same message only once.

This commit moves the log rules from arch/arm/boot/Makefile to
arch/arm/Makefile.  I did not delete them completely because *Image
are the final targets that users are interested in.

Without this commit, the log of incremental build is like follows:

$ make ARCH=arm UIMAGE_LOADADDR=0x80208000 uImage
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  Kernel: arch/arm/boot/Image is ready
  Kernel: arch/arm/boot/Image is ready
  Kernel: arch/arm/boot/zImage is ready
  Kernel: arch/arm/boot/Image is ready
  Kernel: arch/arm/boot/zImage is ready
  Image arch/arm/boot/uImage is ready

With this commit, it will look like follows:

$ make ARCH=arm UIMAGE_LOADADDR=0x80208000 uImage
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  Kernel: arch/arm/boot/Image is ready
  Kernel: arch/arm/boot/zImage is ready
  Kernel: arch/arm/boot/uImage is ready

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>