feat(cpufeat): add feature detection for FEAT_CSV2_3

This feature provides support to context save the
SCXTNUM_ELx register. FEAT_CSV2_3 implies the implementation
of FEAT_CSV2_2. FEAT_CSV2_3 is supported in AArch64 state only
and is an optional feature in Arm v8.0 implementations.

This patch adds feature detection for v8.9 feature FEAT_CSV2_3,
adds macros for ID_AA64PFR0_EL1.CSV2 bits [59:56] for detecting
FEAT_CSV2_3 and macro for ENABLE_FEAT_CSV2_3.

Change-Id: Ida9f31e832b5f11bd89eebd6cc9f10ddad755c14
Signed-off-by: Sona Mathew <sonarebecca.mathew@arm.com>
diff --git a/include/arch/aarch32/arch_features.h b/include/arch/aarch32/arch_features.h
index acc1751..a2063f1 100644
--- a/include/arch/aarch32/arch_features.h
+++ b/include/arch/aarch32/arch_features.h
@@ -137,6 +137,7 @@
 static inline bool is_feat_ecv_supported(void) { return false; }
 static inline bool is_feat_ecv_v2_supported(void) { return false; }
 static inline bool is_feat_csv2_2_supported(void) { return false; }
+static inline bool is_feat_csv2_3_supported(void) { return false; }
 static inline bool is_feat_ras_supported(void) { return false; }
 
 /* The following features are supported in AArch64 only. */