powerpc/kconfig: Kill PPC_MULTIPLATFORM

CONFIG_PPC_MULTIPLATFORM is a remain of the pre-powerpc days and isn't
really meaningful anymore. It was basically equivalent to PPC64 || 6xx.

This removes it along with the following changes:

 - 32-bit platforms that relied on PPC32 && PPC_MULTIPLATFORM now rely
   on 6xx which is what they want anyway.

 - A new symbol, PPC_BOOK3S, is defined that represent compliance with
   the "Server" variant of the architecture. This is set when either 6xx
   or PPC64 is set and open the door for future BOOK3E 64-bit.

 - 64-bit platforms that relied on PPC64 && PPC_MULTIPLATFORM now use
   PPC64 && PPC_BOOK3S

 - A separate and selectable CONFIG_PPC_OF_BOOT_TRAMPOLINE option is now
   used to control the use of prom_init.c

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
index b4ab372..68b9b8f 100644
--- a/arch/powerpc/platforms/Kconfig
+++ b/arch/powerpc/platforms/Kconfig
@@ -1,14 +1,5 @@
 menu "Platform support"
 
-config PPC_MULTIPLATFORM
-	bool
-	depends on PPC64 || 6xx
-	default y
-
-config CLASSIC32
-	def_bool y
-	depends on 6xx && PPC_MULTIPLATFORM
-
 source "arch/powerpc/platforms/pseries/Kconfig"
 source "arch/powerpc/platforms/iseries/Kconfig"
 source "arch/powerpc/platforms/chrp/Kconfig"
@@ -32,12 +23,24 @@
 
 config PPC_NATIVE
 	bool
-	depends on PPC_MULTIPLATFORM
+	depends on 6xx || PPC64
 	help
 	  Support for running natively on the hardware, i.e. without
 	  a hypervisor. This option is not user-selectable but should
 	  be selected by all platforms that need it.
 
+config PPC_OF_BOOT_TRAMPOLINE
+	bool "Support booting from Open Firmware or yaboot"
+	depends on 6xx || PPC64
+	default y
+	help
+	  Support from booting from Open Firmware or yaboot using an
+	  Open Firmware client interface. This enables the kernel to
+	  communicate with open firmware to retrieve system informations
+	  such as the device tree.
+
+	  In case of doubt, say Y
+
 config UDBG_RTAS_CONSOLE
 	bool "RTAS based debug console"
 	depends on PPC_RTAS
@@ -71,7 +74,7 @@
 
 config U3_DART
 	bool
-	depends on PPC_MULTIPLATFORM && PPC64
+	depends on PPC64
 	default n
 
 config PPC_RTAS
@@ -188,7 +191,7 @@
 
 config TAU
 	bool "On-chip CPU temperature sensor support"
-	depends on CLASSIC32
+	depends on 6xx
 	help
 	  G3 and G4 processors have an on-chip temperature sensor called the
 	  'Thermal Assist Unit (TAU)', which, in theory, can measure the on-die