[ARM] Orion: move EHCI/I2C/UART peripheral init into board code

This patch moves initialisation of EHCI/I2C/UART platform devices
from the common orion5x_init() into the board support code.

The rationale behind this is that only the board support code knows
whether certain peripherals have been brought out on the board, and
not initialising peripherals that haven't been brought out is
desirable for example:
- to reduce user confusion (e.g. seeing both 'eth0' and 'eth1'
  appear while there is only one ethernet port on the board); and
- to allow for future power savings (peripherals that have not
  been brought out can be clock gated off entirely).

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Acked-by: Russell King <linux@arm.linux.org.uk>