apple-n61: rename from apple-iphone6 and make myself maintainer

The Apple iPhone 6 (apple-iphone6) has the codename N61. To follow general distro policy, this MR changes the device codename in pmaports to reflect that. Also, since the iPhone 6 port and the Apple mainline kernel fork hasn't seen any contributions in a long while and doesn't have a maintainer listed: this MR adds myself (Aster) as the maintainer for both.