Add support for exynos5_ehci in loader

Create new driver which initializes Arndale PHY and calls ehci_init

Reviewed by: hselasky
Submitted by: Wojciech Macek <wma@semihalf.com>
Obtained from: Semihalf
Sponsored by: Juniper Networks Inc.
Differential Revision: https://reviews.freebsd.org/D4192