sign-file,extract-cert: move common SSL helper functions to a header

commit 300e6d41 upstream.

Couple error handling helpers are repeated in both tools, so
move them to a common header.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>