ARM: mach-msm: fix compile fail from system.h fallout

ARM: mach-msm: fix compile fail from system.h fallout

To fix:

  In file included from arm/boot/compressed/misc.c:28:0:
  arm/mach-msm/include/mach/uncompress.h: In function 'putc':
  arch/arm/mach-msm/include/mach/uncompress.h:48:3: error: implicit
  declaration of function 'smp_mb' [-Werror=implicit-function-declaration]

The putc does a cpu_relax which for this platform is smp_mb.

Bisect indicates the 1st failing commit as: ed9683f04ac7 ("Merge tag
'split-asm_system_h...")

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: David Brown <davidb@codeaurora.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>