powerpc: Allow CPU selection of e300core variants

GCC supports -mcpu=e300c2 and -mcpu=e300c3

This patch gives the opportunity to tune kernel to one of
those two types.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/Kconfig.cputype

@@ -144,6 +144,14 @@ config 860_CPU
 	bool "8xx family"
 	depends on PPC_8xx
 
+config E300C2_CPU
+	bool "e300c2 (832x)"
+	depends on PPC_BOOK3S_32
+
+config E300C3_CPU
+	bool "e300c3 (831x)"
+	depends on PPC_BOOK3S_32
+
 endchoice
 
 config TARGET_CPU_BOOL
@@ -160,6 +168,8 @@ config TARGET_CPU
 	default "power8" if POWER8_CPU
 	default "power9" if POWER9_CPU
 	default "860" if 860_CPU
+	default "e300c2" if E300C2_CPU
+	default "e300c3" if E300C3_CPU
 
 config PPC_BOOK3S
 	def_bool y