refactor(plat/arm): use SOC_ID defines

Use the macros that are now defined in include/lib/smccc.h.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I688a76277b729672835d51fafb68d1d6205b6ae4
diff --git a/include/plat/arm/common/smccc_def.h b/include/plat/arm/common/smccc_def.h
index 6e698e5..0f4e573 100644
--- a/include/plat/arm/common/smccc_def.h
+++ b/include/plat/arm/common/smccc_def.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2020-2021, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,7 +9,5 @@
 /* Defines used to retrieve ARM SOC revision */
 #define ARM_SOC_CONTINUATION_CODE	U(0x4)
 #define ARM_SOC_IDENTIFICATION_CODE	U(0x3B)
-#define ARM_SOC_CONTINUATION_SHIFT	U(24)
-#define ARM_SOC_IDENTIFICATION_SHIFT	U(16)
 
 #endif /* SMCCC_DEF_H */