hw/isa: extract FDC37M81X to a separate file

isa-superio.c currently defines a SuperIO chip that is not used
by any other user of the file.  Extract the chip to a separate file.

Reviewed-by: Bernhard Beschow <shentey@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20240213155005.109954-7-pbonzini@redhat.com>
[PMD: Update MAINTAINERS]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index a24c2b5..8920ba4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1357,6 +1357,7 @@
 R: Aurelien Jarno <aurelien@aurel32.net>
 S: Odd Fixes
 F: hw/isa/piix.c
+F: hw/isa/fdc37m81x-superio.c
 F: hw/acpi/piix4.c
 F: hw/mips/malta.c
 F: hw/pci-host/gt64120.c