powerpc: P5020: Remove macro CONFIG_PPC_P5020

Replace CONFIG_PPC_P5020 with ARCH_P5020 in Kconfig and clean up
existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/drivers/net/fm/Makefile b/drivers/net/fm/Makefile
index 46dc6df..15d27b8 100644
--- a/drivers/net/fm/Makefile
+++ b/drivers/net/fm/Makefile
@@ -22,7 +22,7 @@
 obj-$(CONFIG_ARCH_P2041) += p5020.o
 obj-$(CONFIG_ARCH_P3041) += p5020.o
 obj-$(CONFIG_ARCH_P4080) += p4080.o
-obj-$(CONFIG_PPC_P5020) += p5020.o
+obj-$(CONFIG_ARCH_P5020) += p5020.o
 obj-$(CONFIG_PPC_P5040) += p5040.o
 obj-$(CONFIG_PPC_T1040) += t1040.o
 obj-$(CONFIG_PPC_T1042)	+= t1040.o