generic: globally enable CONFIG_PCPU_DEV_REFCNT

generic: globally enable CONFIG_PCPU_DEV_REFCNT

Quoting the kconfig description for CONFIG_PCPU_DEV_REFCNT:

network device refcount are using per cpu variables if this option is
set. This can be forced to N to detect underflows (with a performance
drop).

This was introduced from kernel 5.13 and was wrongly set as disabled.
Some target actually enables it but this should be always enabled unless
refcount needs to be debugged (unlikely for production images)

Enable in generic and drop the entry in every other target.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18174
Signed-off-by: Robert Marko <robimarko@gmail.com>