misc: Update MAINTAINERS with a system tag

The code in system/ currently doesn't have a well-defined tag. Arm
components have traditionally used 'system-arm' and in some cases just
'arm'. This change introduces a separate tag for system software and
related files components.

Change-Id: I5c0ecd057bd65ab9d88c25f7ec7572d6941e41b5
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19931
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index f080550..df52c36 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -88,6 +88,11 @@
 
 stats: Updates to statistics for regressions
 
+system: System boot code and related components
+system-alpha:
+system-arm:
+  Andreas Sandberg <andreas.sandberg@arm.com>
+
 tests: testing changes (not stats updates for tests. See stats:)
   Andreas Sandberg <andreas.sandberg@arm.com>