powerpc/64: Make server perfmon only built on ppc64 server devices

The 64-bit Book-E parts (to date) dont utilize the 'server' class
perfmon.  So building or depending on it makes no sense (and does break
FSL Book-E 64-bit support).  Move the selection of PPC_HAVE_PMU_SUPPORT
to be based on PPC_BOOK3S_64.

Based on a patch from Scott Wood.
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/Kconfig.cputype

 config PPC64
 	bool "64-bit kernel"
 	default n
-	select PPC_HAVE_PMU_SUPPORT
 	help
 	  This option selects whether a 32-bit or a 64-bit kernel
 	  will be built.
@@ -69,6 +68,7 @@ choice
 config PPC_BOOK3S_64
 	bool "Server processors"
 	select PPC_FPU
+	select PPC_HAVE_PMU_SUPPORT
 
 config PPC_BOOK3E_64
 	bool "Embedded processors"