highmem.h

Hi everyone,

I think highmem.h needs to be copied from include/asm-ppc to
include/asm-powerpc.  For instance, if you include linux/skbuff.h,
it includes linux/highmem.h.  If CONFIG_HIGHMEM is enabled (which is
possible on PPC32), then linux/highmem.h includes asm/highmem.h
which isn't currently included in include/asm-powerpc.

Am I overlooking something here?  For what it's worth, I noticed
this while building the sheep module in MOL.

-Joe