lib: crypto: import pkcs7_verify.c from linux

The file, pkcs7_verify.c, will now be imported from linux code
(crypto/asymmetric_keys/pkcs7_verify.c in 5.7) and modified to fit
into U-Boot environment.

In particular, pkcs7_verify_one() function will be used in a later patch
to rework signature verification logic aiming to support intermediate
certificates in "chain of trust."

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
diff --git a/lib/crypto/Kconfig b/lib/crypto/Kconfig
index 2b221b9..6369baf 100644
--- a/lib/crypto/Kconfig
+++ b/lib/crypto/Kconfig
@@ -49,4 +49,7 @@
 	  This option provides support for parsing PKCS#7 format messages for
 	  signature data and provides the ability to verify the signature.
 
+config PKCS7_VERIFY
+	bool
+
 endif # ASYMMETRIC_KEY_TYPE