postfix: add new recipe

Postfix is Wietse Venema's mail server that started life at IBM
research as an alternative to the widely-used Sendmail program.

Postfix attempts to be fast, easy to administer, and secure.
The outside has a definite Sendmail-ish flavor, but the inside
is completely different.

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>