powerpc: T1024: Remove macro CONFIG_PPC_T1024

Replace CONFIG_PPC_T1024 with ARCH_T1024 in Kconfig and clean up
existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/configs/T1024RDB_SECURE_BOOT_defconfig b/configs/T1024RDB_SECURE_BOOT_defconfig
index 50b5993..806cc21 100644
--- a/configs/T1024RDB_SECURE_BOOT_defconfig
+++ b/configs/T1024RDB_SECURE_BOOT_defconfig
@@ -6,7 +6,7 @@
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_STDOUT_VIA_ALIAS=y
-CONFIG_SYS_EXTRA_OPTIONS="PPC_T1024,T1024RDB,SECURE_BOOT"
+CONFIG_SYS_EXTRA_OPTIONS="T1024RDB,SECURE_BOOT"
 CONFIG_BOOTDELAY=10
 CONFIG_SILENT_CONSOLE=y
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y