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/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 5550687..62c0dec 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -150,6 +150,7 @@
 	bool "Support P1024RDB"
 	select SUPPORT_SPL
 	select SUPPORT_TPL
+	select ARCH_P1024
 
 config TARGET_P1025RDB
 	bool "Support P1025RDB"
@@ -297,6 +298,9 @@
 config ARCH_P1023
 	bool
 
+config ARCH_P1024
+	bool
+
 source "board/freescale/b4860qds/Kconfig"
 source "board/freescale/bsc9131rdb/Kconfig"
 source "board/freescale/bsc9132qds/Kconfig"