armv8: ls1046a: Convert CONFIG_LS1046A to Kconfig option ARCH_LS1046A

Move this option to Kconfig and clean up existing uses.

Signed-off-by: York Sun <york.sun@nxp.com>
CC: Mingkai Hu <mingkai.hu@nxp.com>
CC: Gong Qianyu <Qianyu.Gong@nxp.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/cpu/armv8/fsl-layerscape/Makefile b/arch/arm/cpu/armv8/fsl-layerscape/Makefile
index 8c1317f..f9590af 100644
--- a/arch/arm/cpu/armv8/fsl-layerscape/Makefile
+++ b/arch/arm/cpu/armv8/fsl-layerscape/Makefile
@@ -34,6 +34,6 @@
 obj-$(CONFIG_SYS_HAS_SERDES) += ls1012a_serdes.o
 endif
 
-ifneq ($(CONFIG_LS1046A),)
+ifneq ($(CONFIG_ARCH_LS1046A),)
 obj-$(CONFIG_SYS_HAS_SERDES) += ls1046a_serdes.o
 endif