powerpc: Move prom_init() out of asm-prototypes.h

This is the end of the work started with commit 76222808 ("powerpc:
Move C prototypes out of asm-prototypes.h")

Now that asm/machdep.h doesn't include asm/setup.h anymore, there are
no conflicts anymore with the function prom_init() defined in
drivers/gpu/drm/nouveau/nvkm/subdev/bios/shadowrom.o

So we can move it to asm/setup.h
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e111e4f0addb0fa810d5f6a71d3b8e62c0b53492.1654966508.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/asm-prototypes.h

@@ -34,12 +34,6 @@ int64_t __opal_call(int64_t a0, int64_t a1, int64_t a2, int64_t a3,
 		    int64_t a4, int64_t a5, int64_t a6, int64_t a7,
 		    int64_t opcode, uint64_t msr);
 
-/* prom_init (OpenFirmware) */
-unsigned long __init prom_init(unsigned long r3, unsigned long r4,
-			       unsigned long pp,
-			       unsigned long r6, unsigned long r7,
-			       unsigned long kbase);
-
 /* misc runtime */
 extern u64 __bswapdi2(u64);
 extern s64 __lshrdi3(s64, int);

arch/powerpc/include/asm/setup.h

@@ -85,6 +85,11 @@ void __init machine_init(u64 dt_ptr);
 void __init early_setup(unsigned long dt_ptr);
 void early_setup_secondary(void);
 
+/* prom_init (OpenFirmware) */
+unsigned long __init prom_init(unsigned long r3, unsigned long r4,
+			       unsigned long pp, unsigned long r6,
+			       unsigned long r7, unsigned long kbase);
+
 #endif /* !__ASSEMBLY__ */
 
 #endif	/* _ASM_POWERPC_SETUP_H */