bosch: Add initial board support for ACC

The Bosch ACC (Air Center Control) Board is based on the i.MX6D.

The device tree is copied from Linux, see [1]. The only difference
compared to the Linux DT is the removal of usbphynop properties. They are
defined in the Linux version of imx6qdl.dtsi, but not in the u-boot
version.

[1] Commit 6192cf8ac082 from
    git.kernel.org/pub/scm/linux/kernel/git/shawnguo/linux.git

Signed-off-by: Philip Oberfichtner <pro@denx.de>