HID: split picolcd's operation_mode sysfs attribute

Original operation_mode sysfs attribute accepts the operation mode
as main value with an option delay as second value to change
the start-up delay on mode change.

As it is preferred to have exactly one value per sysfs attribute,
extract this delay into a separate sysfs attribute called
operation_mode_delay.

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>