serial: stm32: defer sysrq processing

Use the uart_unlock_and_check_sysrq() helper to defer sysrq processing
until receive processing is done and the port lock has been released.

This allows cleaning up the console_write() implementation by not having
to work around the recursive sysrq case (by dropping locking completely)
and also makes the console code work with PREEMPT_RT by no longer
relying on local_irq_save().

Reviewed-by: Valentin <Caron&lt;valentin.caron@foss.st.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210416140557.25177-4-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>