powerpc: P5040: Remove macro CONFIG_P5040

Replace CONFIG_P5040 with ARCH_P5040 in Kconfig and clean up
existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/include/asm/config_mpc85xx.h b/arch/powerpc/include/asm/config_mpc85xx.h
index 496b845..23ee8f9 100644
--- a/arch/powerpc/include/asm/config_mpc85xx.h
+++ b/arch/powerpc/include/asm/config_mpc85xx.h
@@ -465,7 +465,7 @@
 #define CONFIG_SYS_FSL_ERRATUM_A006261
 #define CONFIG_SYS_FSL_A004447_SVR_REV	0x20
 
-#elif defined(CONFIG_PPC_P5040)
+#elif defined(CONFIG_ARCH_P5040)
 #define CONFIG_SYS_PPC64
 #define CONFIG_SYS_FSL_QORIQ_CHASSIS1
 #define CONFIG_FSL_CORENET		/* Freescale CoreNet platform */