ARM i.MX ehci: do ehci init in board specific functions

The mxc-ehci driver calls SoC specific phy initialization right after
calling board specific initialization. To offer greater flexibility for
boards to setup the phy and to get rid of some unnecessary flags in
platform data this patch lets the boards call the SoC specific phy
initialization and remove it from the driver.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>