ehci-octeon driver used a 64-bit dma_mask. With removal of ehci-octeon
and usage of ehci-platform ehci dma_mask is now limited to 32 bits
(coerced in ehci_platform_probe).

Provide a flag in ehci platform data to allow use of 64 bits for
dma_mask.

Cc: David Daney <david.daney@cavium.com>
Cc: Alex Smith <alex.smith@imgtec.com>
Signed-off-by: NAndreas Herrmann <andreas.herrmann@caviumnetworks.com>
Tested-by: NAaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>