crypto: Enable context analysis

Enable context analysis for crypto subsystem.

This demonstrates a larger conversion to use Clang's context
analysis. The benefit is additional static checking of locking rules,
along with better documentation.

Note the use of the __acquire_ret macro how to define an API where a
function returns a pointer to an object (struct scomp_scratch) with a
lock held. Additionally, the analysis only resolves aliases where the
analysis unambiguously sees that a variable was not reassigned after
initialization, requiring minor code changes.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251219154418.3592607-36-elver@google.com

crypto/api.c

@@ -57,6 +57,7 @@ EXPORT_SYMBOL_GPL(crypto_mod_put);
 
 static struct crypto_alg *__crypto_alg_lookup(const char *name, u32 type,
 					      u32 mask)
+	__must_hold_shared(&crypto_alg_sem)
 {
 	struct crypto_alg *q, *alg = NULL;
 	int best = -2;