armv8: ls2080a: Move CONFIG_FSL_MC_ENET to Kconfig

Use Kconfig option instead of config macro in header file.
Clean up existing usage.

Signed-off-by: York Sun <york.sun@nxp.com>

arch/arm/cpu/armv8/fsl-layerscape/Kconfig

@@ -89,6 +89,14 @@ config FSL_LSCH3
 	select SYS_FSL_SRDS_1
 	select SYS_HAS_SERDES
 
+config FSL_MC_ENET
+	bool "Management Complex network"
+	depends on ARCH_LS2080A
+	default y
+	select RESV_RAM
+	help
+	  Enable Management Complex (MC) network
+
 menu "Layerscape architecture"
 	depends on FSL_LSCH2 || FSL_LSCH3