drivers: stmmac: set mac_managed_pm to true to fix mdio resume warning

This patch is to fix the following warning:

WARNING: CPU: 3 PID: 961 at drivers/net/phy/phy_device.c:322 mdio_bus_phy_resume+0x10c/0x11c

 CPU: 3 PID: 961 Comm: rtcwake Tainted: G        W         5.15.68-yocto-standard #1
 Hardware name: NXP S32G399A-RDB3 (DT)
 pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : mdio_bus_phy_resume+0x10c/0x11c
 lr : dpm_run_callback+0x74/0xc0
 sp : ffffffc00dbe3a40
 x29: ffffffc00dbe3a40 x28: ffffff880344d260 x27: ffffffc009f24558
 x26: ffffffc009506828 x25: ffffffc009da6594 x24: ffffffc009fc3948
 x23: 0000000000000010 x22: ffffff880bf04120 x21: 0000000000000010
 x20: ffffff880bf04000 x19: ffffff880bf04000 x18: ffffffffffffffff
 x17: 0000000000000001 x16: 00006554f77f3812 x15: ffffffc00aaf1601
 x14: 0000000000000000 x13: ffffffc00aaf15fe x12: ffffffffffffffff
 x11: 00000000000000f4 x10: 00000000074d40f7 x9 : ffffffc008af1ce4
 x8 : ffffffc00dbe3710 x7 : 0000000000000000 x6 : 0000000000000001
 x5 : ffffffc009d81000 x4 : 0000000000000001 x3 : ffffffc0097bc008
 x2 : ffffff880a055a40 x1 : 0000000000000005 x0 : 0000000000000004
 Call trace:
  mdio_bus_phy_resume+0x10c/0x11c
  dpm_run_callback+0x74/0xc0
  device_resume+0xa0/0x1f4
  dpm_resume+0x11c/0x290
  dpm_resume_end+0x20/0x40
  suspend_devices_and_enter+0x1a8/0x20c
  enter_state+0x148/0x1dc
  pm_suspend+0x60/0xf0
  state_store+0x94/0x120
  kobj_attr_store+0x18/0x30
  sysfs_kf_write+0x54/0x80
  kernfs_fop_write_iter+0x128/0x1c0
  new_sync_write+0xf0/0x190
  vfs_write+0x1c4/0x220
  ksys_write+0x70/0x100
  __arm64_sys_write+0x24/0x30
  invoke_syscall+0x5c/0x130
  el0_svc_common.constprop.0+0x68/0x124
  do_el0_svc+0x4c/0xb0
  el0_svc+0x54/0x130
  el0t_64_sync_handler+0xa4/0x130
  el0t_64_sync+0x1a0/0x1a4

The reason is that, the commit 47ac7b2f ("net: phy: Warn about incorrect
mdio_bus_phy_resume() state") introduced a WARN when phy state is not in the
states: PHY_HALTED, PHY_READY and PHY_UP. When GMAC resumes, there have port
in PHY_NOLINK state, so the above warning comes out. So set mac_managed_pm
be true to tell mdio that the phy resume/suspend is managed by the mac, then
the issue will be fixed.

Signed-off-by: Zhantao Tang <zhantao.tang@windriver.com>