Similar to the existing helpers for the Clause 22 registers add helper
mii_10gbt_stat_mod_linkmode_lpa_t.

Note that this helper is defined in linux/mdio.h, not like the
Clause 22 helpers in linux/mii.h. Reason is that the Clause 45 register
constants are defined in uapi/linux/mdio.h. And uapi/linux/mdio.h
includes linux/mii.h before defining the C45 register constants.

v2:
- remove helpers that don't have users in this series
Signed-off-by: NHeiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>