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/arch/powerpc/include/asm/fsl_secure_boot.h b/arch/powerpc/include/asm/fsl_secure_boot.h
index 38b666c..47c3d98 100644
--- a/arch/powerpc/include/asm/fsl_secure_boot.h
+++ b/arch/powerpc/include/asm/fsl_secure_boot.h
@@ -60,7 +60,7 @@
 
 #if defined(CONFIG_ARCH_P3041)	||	\
 	defined(CONFIG_ARCH_P4080) ||	\
-	defined(CONFIG_PPC_P5020) ||	\
+	defined(CONFIG_ARCH_P5020) ||	\
 	defined(CONFIG_PPC_P5040) ||	\
 	defined(CONFIG_ARCH_P2041)
 	#define	CONFIG_FSL_TRUST_ARCH_v1