can: flexcan: enable RX FIFO after FRZ/HALT valid

RX FIFO enable failed could happen when do system reboot stress test:

[    0.303958] flexcan 5a8d0000.can: 5a8d0000.can supply xceiver not found, using dummy regulator
[    0.304281] flexcan 5a8d0000.can (unnamed net_device) (uninitialized): Could not enable RX FIFO, unsupported core
[    0.314640] flexcan 5a8d0000.can: registering netdev failed
[    0.320728] flexcan 5a8e0000.can: 5a8e0000.can supply xceiver not found, using dummy regulator
[    0.320991] flexcan 5a8e0000.can (unnamed net_device) (uninitialized): Could not enable RX FIFO, unsupported core
[    0.331360] flexcan 5a8e0000.can: registering netdev failed
[    0.337444] flexcan 5a8f0000.can: 5a8f0000.can supply xceiver not found, using dummy regulator
[    0.337716] flexcan 5a8f0000.can (unnamed net_device) (uninitialized): Could not enable RX FIFO, unsupported core
[    0.348117] flexcan 5a8f0000.can: registering netdev failed

RX FIFO should be enabled after the FRZ/HALT are valid. But the current
code enable RX FIFO and FRZ/HALT at the same time.

Fixes: e955cead

 ("CAN: Add Flexcan CAN controller driver")
Link: https://lore.kernel.org/r/20210218110037.16591-3-qiangqing.zhang@nxp.com
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>