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/configs/Cyrus_P5020_defconfig b/configs/Cyrus_P5020_defconfig
index 5eb5660..94fc387 100644
--- a/configs/Cyrus_P5020_defconfig
+++ b/configs/Cyrus_P5020_defconfig
@@ -5,7 +5,7 @@
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
-CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,SYS_TEXT_BASE=0xFFF40000,PPC_P5020"
+CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,SYS_TEXT_BASE=0xFFF40000,ARCH_P5020"
 CONFIG_BOOTDELAY=10
 CONFIG_CONSOLE_MUX=y
 CONFIG_HUSH_PARSER=y