moving include/asm-ppc/platforms

With the addition of -I$(TOPDIR)/arch/$(ARCH) to the compilation flags
for the kernel, we can now move the platform-specific header files
from include/asm-ppc/platforms to arch/ppc/platforms, which is where I
think they belong.  That does require changing <asm/platforms/blah.h>
to <platforms/blah.h>, but that is not a big job because these headers
tend to get included in only a few places.

For 2.4 we will keep the ugly lists of ifdefs in places like serial.h
and mpc8xx.h.  For 2.5 we should change over to using a mechanism to
copy an appropriate platform-dependent file to arch/ppc/platform.h.

Once we have moved include/asm-ppc/platforms/*.h to arch/ppc/platforms,
it will just about be time to do a big merge from devel into
linuxppc_2_4 and thence to Marcelo's tree.

Paul.

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