ppc: Remove CHRP, POWER3 and POWER4 support from arch/ppc

32-bit CHRP machines are now supported only in arch/powerpc, as are
all 64-bit PowerPC processors.  This means that we don't use
Open Firmware on any platform in arch/ppc any more.

This makes PReP support a single-platform option like every other
platform support option in arch/ppc now, thus CONFIG_PPC_MULTIPLATFORM
is gone from arch/ppc.  CONFIG_PPC_PREP is the option that selects
PReP support and is generally what has replaced
CONFIG_PPC_MULTIPLATFORM within arch/ppc.

_machine is all but dead now, being #defined to 0.

Updated Makefiles, comments and Kconfig options generally to reflect
these changes.

Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/processor.h b/include/asm-powerpc/processor.h
index 1c64a21..a64198f 100644
--- a/include/asm-powerpc/processor.h
+++ b/include/asm-powerpc/processor.h
@@ -53,10 +53,7 @@
 #define platform_is_pseries()	(_machine == PLATFORM_PSERIES || \
 				 _machine == PLATFORM_PSERIES_LPAR)
 
-#if defined(CONFIG_PPC_MULTIPLATFORM)
-extern int _machine;
-
-#ifdef CONFIG_PPC32
+#ifdef CONFIG_PPC_PREP
 
 /* what kind of prep workstation we are */
 extern int _prep_type;
@@ -70,7 +67,10 @@
 extern unsigned char ucBoardRev;
 extern unsigned char ucBoardRevMaj, ucBoardRevMin;
 
-#endif /* CONFIG_PPC32 */
+#endif /* CONFIG_PPC_PREP */
+
+#if defined(CONFIG_PPC_MULTIPLATFORM)
+extern int _machine;
 
 #elif defined(CONFIG_PPC_ISERIES)
 /*