We originally added asm-prototypes.h in commit 42f5b4ca ("powerpc:
Introduce asm-prototypes.h"). It's purpose was for prototypes of C
functions that are only called from asm, in order to fix sparse
warnings about missing prototypes.

A few months later Nick added a different use case in
commit 4efca4ed ("kbuild: modversions for EXPORT_SYMBOL() for asm")
for C prototypes for exported asm functions. This is basically the
inverse of our original usage.

Since then we've added various prototypes to asm-prototypes.h for both
reasons, meaning we now need to unstitch it all.

Dispatch prototypes of C functions into relevant headers and keep
only the prototypes for functions defined in assembly.

For the time being, leave prom_init() there because moving it
into asm/prom.h or asm/setup.h conflicts with
drivers/gpu/drm/nouveau/nvkm/subdev/bios/shadowrom.o
This will be fixed later by untaggling asm/pci.h and asm/prom.h
or by renaming the function in shadowrom.c
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/62d46904eca74042097acf4cb12c175e3067f3d1.1646413435.git.christophe.leroy@csgroup.eu