powerpc: P2020: Remove macro CONFIG_P2020

Replace CONFIG_P2020 with ARCH_P2020 in Kconfig and clean up
existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/board/xes/common/Makefile b/board/xes/common/Makefile
index 1b2ec5c..db1f029f 100644
--- a/board/xes/common/Makefile
+++ b/board/xes/common/Makefile
@@ -8,7 +8,7 @@
 obj-$(CONFIG_FSL_PCI_INIT)	+= fsl_8xxx_pci.o
 obj-$(CONFIG_ARCH_MPC8572)		+= fsl_8xxx_clk.o
 obj-$(CONFIG_MPC86xx)		+= fsl_8xxx_clk.o
-obj-$(CONFIG_P2020)		+= fsl_8xxx_clk.o
+obj-$(CONFIG_ARCH_P2020)		+= fsl_8xxx_clk.o
 obj-$(CONFIG_MPC85xx)		+= fsl_8xxx_misc.o board.o
 obj-$(CONFIG_MPC86xx)		+= fsl_8xxx_misc.o board.o
 obj-$(CONFIG_NAND_ACTL)	+= actl_nand.o