greybus: bootrom: Wait for 10 seconds for mode-switch

The greybus SVC core handles events from the SVC serially today. In some
cases the SVC operations may take too long, for example trying to
activate a dummy interface. If another interface receives a mode-switch
mailbox event in that time, the SVC core wouldn't be able to process it
in quickly enough and bootrom driver will print following error:

bootrom 1-3.3.1: Timed out waiting for Interface Mode Switch from the Module

This can be reproduced easily by attaching a 2x2 module along with any
other normal module like camera or speaker, and doing a unipro_reset
from userspace.

The logs suggest this time to be around 6-7 seconds in most of the
cases. Attaching multiple modules with dummy interfaces may make this
worst.

Lets increase the timeout from 5 to 10 seconds for now, also add a FIXME
for the same.

Testing Done: Tested on EVT 2.0 with camera and a 2x2 module.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>