ARM: mmp: remove obsolete config USB_EHCI_MV_U2O

Commit 77acc85c ("ARM: mmp: remove device definitions") and commit
06f11dfb ("ARM: mmp: remove all board files") remove mach-mmp's device
definitions and the board file for the Marvell PXA910-based TTC_DKB
Development Platform. With that removal, all references to the config
USB_EHCI_MV_U2O are gone. The config has no remaining effect and can be
deleted.

Remove the obsolete config USB_EHCI_MV_U2O.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>