powerpc/cell: Add missing #include for oprofile

arch/powerpc/oprofile/cell/spu_profiler.c is missing a asm/time.h
include which is required for ppc_proc_freq.  This can cause compile
failures for some config combinations.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>