module: Give 'enum pkey_id_type' a more specific name

module: Give 'enum pkey_id_type' a more specific name

This enum originates in generic cryptographic code and has a very
generic name. Nowadays it is only used for module signatures.

As this enum is going to be exposed in a UAPI header, give it a more
specific name for clarity and consistency.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>