powerpc: P1024: Remove CONFIG_P1024

Replace CONFIG_P1024 with ARCH_P1024 in Kconfig and clean up
existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Makefile b/arch/powerpc/cpu/mpc85xx/Makefile
index 515647d..239cf41 100644
--- a/arch/powerpc/cpu/mpc85xx/Makefile
+++ b/arch/powerpc/cpu/mpc85xx/Makefile
@@ -78,7 +78,7 @@
 obj-$(CONFIG_ARCH_P1021)	+= p1021_serdes.o
 obj-$(CONFIG_ARCH_P1022)	+= p1022_serdes.o
 obj-$(CONFIG_ARCH_P1023)	+= p1023_serdes.o
-obj-$(CONFIG_P1024)	+= p1021_serdes.o
+obj-$(CONFIG_ARCH_P1024)	+= p1021_serdes.o
 obj-$(CONFIG_P1025)	+= p1021_serdes.o
 obj-$(CONFIG_P2010)	+= p2020_serdes.o
 obj-$(CONFIG_P2020)	+= p2020_serdes.o