x86/cet: Remove XEN_SHSTK's dependency on EXPERT

CET-SS hardware is now available from multiple vendors, the feature has
downstream users, and was declared security supported in XSA-398.

Enable it by default.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

xen/arch/x86/Kconfig

@@ -117,8 +117,8 @@ config HVM
 	  If unsure, say Y.
 
 config XEN_SHSTK
-	bool "Supervisor Shadow Stacks (EXPERT)"
-	depends on HAS_AS_CET_SS && EXPERT
+	bool "Supervisor Shadow Stacks"
+	depends on HAS_AS_CET_SS
 	default y
 	---help---
 	  Control-flow Enforcement Technology (CET) is a set of features in