refactor(el3-runtime): add prepare_el3_entry func

In the next patch we add an extra step of setting the PSTATE
registers to a known state on el3 entry. In this patch we create
the function prepare_el3_entry to wrap the steps needed for before
el3 entry. For now this is only save_gp_pmcr_pauth_regs.

Change-Id: Ie26dc8d89bfaec308769165d2649e84d41be196c
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
diff --git a/bl1/aarch64/bl1_exceptions.S b/bl1/aarch64/bl1_exceptions.S
index 9dc9e6c..c54219f 100644
--- a/bl1/aarch64/bl1_exceptions.S
+++ b/bl1/aarch64/bl1_exceptions.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2020, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2022, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -224,7 +224,7 @@
 	 * TODO: Revisit to store only SMCCC specified registers.
 	 * -----------------------------------------------------
 	 */
-	bl	save_gp_pmcr_pauth_regs
+	bl	prepare_el3_entry
 
 #if ENABLE_PAUTH
 	/* -----------------------------------------------------