powerpc: Make COFF zImages for old 32-bit powermacs

This adds code to build zImage.coff and/or zImage.initrd.coff when
CONFIG_PPC32 and CONFIG_PPC_PMAC are defined.  It also restructures
the OF client code and adds some workarounds for OF quirks on the
older machines.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/boot/stdio.h

@@ -7,10 +7,4 @@ extern int sprintf(char *buf, const char *fmt, ...);
 
 extern int vsprintf(char *buf, const char *fmt, va_list args);
 
-extern int putc(int c, void *f);
-extern int putchar(int c);
-extern int getchar(void);
-
-extern int fputs(char *str, void *f);
-
 #endif				/* _PPC_BOOT_STDIO_H_ */