refactor(cpufeat): separate the EL2 and EL3 enablement code

Combining the EL2 and EL3 enablement code necessitates that it must be
called at el3_exit, which is the only place with enough context to make
the decision of what needs to be set.
Decouple them to allow them to be called from elsewhere.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: I147764c42771e7d4100699ec8fae98dac0a505c0
diff --git a/lib/extensions/sys_reg_trace/aarch32/sys_reg_trace.c b/lib/extensions/sys_reg_trace/aarch32/sys_reg_trace.c
index b3f44b7..6da504e 100644
--- a/lib/extensions/sys_reg_trace/aarch32/sys_reg_trace.c
+++ b/lib/extensions/sys_reg_trace/aarch32/sys_reg_trace.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, Arm Limited. All rights reserved.
+ * Copyright (c) 2021-2023, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -10,7 +10,7 @@
 #include <arch_helpers.h>
 #include <lib/extensions/sys_reg_trace.h>
 
-void sys_reg_trace_enable(void)
+void sys_reg_trace_init_el3(void)
 {
 	uint32_t val;