net: phy: disregard "Clause 22 registers present" bit in get_phy_c45_devs_in_pkg

Bit 0 in register 1.5 doesn't represent a device but is a flag that
Clause 22 registers are present. Therefore disregard this bit when
populating the device list. If code needs this information it
should read register 1.5 directly instead of accessing the device
list.
Because this bit doesn't represent a device don't define a
MDIO_MMD_XYZ constant, just define a MDIO_DEVS_XYZ constant for
the flag in the device list bitmap.

v2:
- make masking of bit 0 more explicit
- improve commit message

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>