g10: Unattended key generation "Key-Grip" and "Subkey-Grip".

* g10/keygen.c (pSUBKEYGRIP): New.
(read_parameter_file): Add "Key-Grip" and "Subkey-Grip".
(do_generate_keypair): Support pSUBKEYGRIP.

In the manual, it says "Key-Grip". gpgsm also supports "Key-Grip".
Adding "Subkey-Grip" now, adding "Key-Grip" makes sense.

(cherry picked from commit 6c63a04569c07c9c2817c7c530a92ccfa58155cc)

• GnuPG-bug-id: T3478
• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>