powerpc: Set default CPU type to POWER8 for little endian builds

We supported POWER7 CPUs for bootstrapping little endian, but the
target was always POWER8. Now that POWER7 specific issues are
impacting performance, change the default target to POWER8.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/Kconfig.cputype

@@ -87,6 +87,7 @@ endchoice
 choice
 	prompt "CPU selection"
 	depends on PPC64
+	default POWER8_CPU if CPU_LITTLE_ENDIAN
 	default GENERIC_CPU
 	help
 	  This will create a kernel which is optimised for a particular CPU.