powerpc: T4240: Remove macro CONFIG_PPC_T4240

Use CONFIG_ARCH_T4240 from Kconfig instead.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/drivers/net/fm/Makefile b/drivers/net/fm/Makefile
index 43d6406..4bfadaa 100644
--- a/drivers/net/fm/Makefile
+++ b/drivers/net/fm/Makefile
@@ -32,7 +32,7 @@
 obj-$(CONFIG_ARCH_T1024) += t1024.o
 obj-$(CONFIG_ARCH_T2080) += t2080.o
 obj-$(CONFIG_ARCH_T2081) += t2080.o
-obj-$(CONFIG_PPC_T4240) += t4240.o
+obj-$(CONFIG_ARCH_T4240) += t4240.o
 obj-$(CONFIG_ARCH_T4160) += t4240.o
 obj-$(CONFIG_PPC_T4080) += t4240.o
 obj-$(CONFIG_ARCH_B4420) += b4860.o