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/drivers/net/fm/Makefile b/drivers/net/fm/Makefile
index 344fbe2..316fef4 100644
--- a/drivers/net/fm/Makefile
+++ b/drivers/net/fm/Makefile
@@ -39,4 +39,4 @@
 obj-$(CONFIG_PPC_B4420) += b4860.o
 obj-$(CONFIG_PPC_B4860) += b4860.o
 obj-$(CONFIG_LS1043A)	+= ls1043.o
-obj-$(CONFIG_LS1046A)	+= ls1046.o
+obj-$(CONFIG_ARCH_LS1046A)	+= ls1046.o