ACPI: SPCR: Support Precise Baud Rate field

The Microsoft Serial Port Console Redirection (SPCR) specification
revision 1.09 comprises additional field: Precise Baud Rate [1].

It is used to describe non-traditional baud rates (such as those
used by high-speed UARTs).

It contains a specific non-zero baud rate which overrides the value
of the Configured Baud Rate field. If this field is zero or not
present, Configured Baud Rate is used.

Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table

 [1]
Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
Link: https://patch.msgid.link/20250913070815.16758-1-cp0613@linux.alibaba.com


[ rjw: Corrected typo in the subject ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>