certs: Fix build error when PKCS#11 URI contains semicolon

certs: Fix build error when PKCS#11 URI contains semicolon

When CONFIG_MODULE_SIG_KEY is PKCS#11 URI (pkcs11:*) and contains a
semicolon, signing_key.x509 fails to build:

  certs/extract-cert pkcs11:token=foo;object=bar;pin-value=1111 certs/signing_key.x509
  Usage: extract-cert <source> <dest>

Add quotes to the extract-cert argument to avoid splitting by the shell.

This approach was suggested by Masahiro Yamada <masahiroy@kernel.org>.

Fixes: 129ab0d2d9f3 ("kbuild: do not quote string values in include/config/auto.conf")
Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>