powerpc: Use -mcpu=power7 on ppc64 little endian builds

Using -mcpu=power7 allows gcc to use a number of new instructions
including 64 bit byte reversed loads.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/Kconfig.cputype

@@ -93,22 +93,23 @@ choice
 
 config GENERIC_CPU
 	bool "Generic"
+	depends on !CPU_LITTLE_ENDIAN
 
 config CELL_CPU
 	bool "Cell Broadband Engine"
-	depends on PPC_BOOK3S_64
+	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN
 
 config POWER4_CPU
 	bool "POWER4"
-	depends on PPC_BOOK3S_64
+	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN
 
 config POWER5_CPU
 	bool "POWER5"
-	depends on PPC_BOOK3S_64
+	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN
 
 config POWER6_CPU
 	bool "POWER6"
-	depends on PPC_BOOK3S_64
+	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN
 
 config POWER7_CPU
 	bool "POWER7"