dovecot: add PKG_LICENSE information

Signed-off-by: Ian Leonard <antonlacon@gmail.com>

mail/dovecot/Makefile

@@ -14,6 +14,8 @@ PKG_RELEASE:=1
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=http://www.dovecot.org/releases/2.2
 PKG_MD5SUM:=a3eb1c0b1822c4f2b0fe9247776baa71
+PKG_LICENSE:=LGPL-2.1 MIT BSD-3-Clause Unique
+PKG_LICENSE_FILES:=COPYING COPYING.LGPL COPYING.MIT
 
 PKG_BUILD_DEPENDS:=libiconv