can: flexcan: flexcan_close(): change order if commands to properly shut down the controller

There haven been reports, that the flexcan_close() soradically hangs during
simultanious ifdown, sending of CAN messages and probably open CAN bus:

| (__schedule) from [<808bbd34>] (schedule+0x90/0xb8)
| (schedule) from [<808bf274>] (schedule_timeout+0x1f8/0x24c)
| (schedule_timeout) from [<8016be44>] (msleep+0x18/0x1c)
| (msleep) from [<80746a64>] (napi_disable+0x60/0x70)
| (napi_disable) from [<8052fdd0>] (flexcan_close+0x2c/0x140)
| (flexcan_close) from [<80744930>] (__dev_close_many+0xb8/0xd8)
| (__dev_close_many) from [<8074db9c>] (__dev_change_flags+0xd0/0x1a0)
| (__dev_change_flags) from [<8074dc84>] (dev_change_flags+0x18/0x48)
| (dev_change_flags) from [<80760c24>] (do_setlink+0x44c/0x7b4)
| (do_setlink) from [<80761560>] (rtnl_newlink+0x374/0x68c)

I was unable to reproduce the issue, but a cleanup of the flexcan close
sequence has probably fixed the problem at the reporting user.

This patch changes the sequence in flexcan_close() to:
- stop the TX queue
- disable the interrupts on the chip level and wait via free_irq()
  synchronously for the interrupt handler to finish
- disable RX offload, which disables synchronously NAPI
- disable the flexcan on the chip level
- free RX offload
- disable the transceiver
- close the CAN device
- disable the clocks

Link: https://lore.kernel.org/r/20201119100917.3013281-6-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

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