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/include/lib/extensions/mpam.h b/include/lib/extensions/mpam.h
index 4327278..e5438ce 100644
--- a/include/lib/extensions/mpam.h
+++ b/include/lib/extensions/mpam.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2023, Arm Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -10,11 +10,15 @@
 #include <stdbool.h>
 
 #if ENABLE_MPAM_FOR_LOWER_ELS
-void mpam_enable(bool el2_unused);
+void mpam_init_el3(void);
+void mpam_init_el2_unused(void);
 #else
-static inline void mpam_enable(bool el2_unused)
+static inline void mpam_init_el3(void)
 {
 }
-#endif
+static inline void mpam_init_el2_unused(void)
+{
+}
+#endif /* ENABLE_MPAM_FOR_LOWER_ELS */
 
 #endif /* MPAM_H */