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/sve.h b/include/lib/extensions/sve.h
index 1faed2d..fc76a16 100644
--- a/include/lib/extensions/sve.h
+++ b/include/lib/extensions/sve.h
@@ -11,11 +11,15 @@
 
 #if (ENABLE_SME_FOR_NS || ENABLE_SVE_FOR_NS)
 void sve_enable(cpu_context_t *context);
+void sve_init_el2_unused(void);
 void sve_disable(cpu_context_t *context);
 #else
 static inline void sve_enable(cpu_context_t *context)
 {
 }
+static inline void sve_init_el2_unused(void)
+{
+}
 static inline void sve_disable(cpu_context_t *context)
 {
 }