net: stmmac: dwmac-sun8i: Balance syscon (de)initialization

Previously, sun8i_dwmac_set_syscon was called from a chain of functions
in several different files:
    sun8i_dwmac_probe
      stmmac_dvr_probe
        stmmac_hw_init
          stmmac_hwif_init
            sun8i_dwmac_setup
              sun8i_dwmac_set_syscon
which made the lifetime of the syscon values hard to reason about. Part
of the problem is that there is no similar platform driver callback from
stmmac_dvr_remove. As a result, the driver unset the syscon value in
sun8i_dwmac_exit, but this leaves it uninitialized after a suspend/
resume cycle. It was also unset a second time (outside sun8i_dwmac_exit)
in the probe error path.

Move the init to the earliest available place in sun8i_dwmac_probe
(after stmmac_probe_config_dt, which initializes plat_dat), and the
deinit to the corresponding position in the cleanup order.

Since priv is not filled in until stmmac_dvr_probe, this requires
changing the sun8i_dwmac_set_syscon parameters to priv's two relevant
members.

Fixes: 9f93ac8d ("net-next: stmmac: Add dwmac-sun8i")
Fixes: 634db83b

 ("net: stmmac: dwmac-sun8i: Handle integrated/external MDIOs")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: David S. Miller <davem@davemloft.net>