arm: Define kconfig symbols used by arm64 cpufeatures

Define kconfig symbols which are used by arm64 cpufeatures to prevent
using undefined symbols and rely on IS_ENABLED returning false.
All the features related to those symbols are unsupported by Xen:
- pointer authentication
- sve
- memory tagging
- branch target identification

Signed-off-by: Bertrand Marquis <bertrand.marquis@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>

xen/arch/arm/Kconfig

@@ -98,6 +98,34 @@ config HARDEN_BRANCH_PREDICTOR
 
 	  If unsure, say Y.
 
+config ARM64_PTR_AUTH
+	def_bool n
+	depends on ARM64
+	help
+	  Pointer authentication support.
+	  This feature is not supported in Xen.
+
+config ARM64_SVE
+	def_bool n
+	depends on ARM64
+	help
+	  Scalar Vector Extension support.
+	  This feature is not supported in Xen.
+
+config ARM64_MTE
+	def_bool n
+	depends on ARM64
+	help
+	  Memory Tagging Extension support.
+	  This feature is not supported in Xen.
+
+config ARM64_BTI
+	def_bool n
+	depends on ARM64
+	help
+	  Branch Target Identification support.
+	  This feature is not supported in Xen.
+
 config TEE
 	bool "Enable TEE mediators support (UNSUPPORTED)" if UNSUPPORTED
 	default n