ehci-platform: Add support for shared reset controllers

Add support for shared platform controllers by using
devm_reset_control_get_shared_by_index instead of
of_reset_control_get_by_index.

Note we use the devm function because there is no
of_reset_control_get_shared_by_index, this also leads
to a nice cleanup of the cleanup code.

This brings the ehci-platform reset handling code inline
with ohci-platform.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>