Convert CONFIG_L2_CACHE to Kconfig

This converts the following to Kconfig:
   CONFIG_L2_CACHE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 721dafc..3651961 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -1297,6 +1297,9 @@
 		Number of TLB CAM entries for Book-E chips. 64 for E500MC,
 		16 for other E500 SoCs.
 
+config L2_CACHE
+	bool "Enable L2 cache support"
+
 if HETROGENOUS_CLUSTERS
 
 config SYS_MAPLE