arm64: dts: imx8qm: Add imx8qm's own pm to avoid panic during startup

Add imx8qm's own pm, otherwise the following panic will
occur during the startup process:

 Kernel panic - not syncing: Asynchronous SError Interrupt
 Hardware name: Freescale i.MX8QM MEK (DT)
 Workqueue: events_unbound deferred_probe_work_func
 Call trace:
  dump_backtrace+0x98/0xf0
  show_stack+0x18/0x24
  dump_stack_lvl+0x60/0xac
  dump_stack+0x18/0x24
  panic+0x340/0x3a0
  nmi_panic+0x8c/0x90
  arm64_serror_panic+0x6c/0x78
  do_serror+0x3c/0x78
  el1h_64_error_handler+0x38/0x50
  el1h_64_error+0x64/0x68
  fsl_edma_chan_mux+0x98/0xdc
  fsl_edma_probe+0x278/0x898
  platform_probe+0x68/0xd8
  really_probe+0x110/0x27c
  __driver_probe_device+0x78/0x12c
  driver_probe_device+0x3c/0x118
  __device_attach_driver+0xb8/0xf8
  bus_for_each_drv+0x84/0xe4
  __device_attach+0xfc/0x18c
  device_initial_probe+0x14/0x20

Fixes: e4d7a330 ("arm64: dts: imx8: add edma[0..3]")
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>