MAINTAINERS: Add usermode related config files

The default-configs/*-linux-user.mak belong to Linux usermode
emulation, and default-configs/*-bsd-user.mak belong to BSD
usermode emulation.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

MAINTAINERS

@@ -1425,11 +1425,13 @@ F: user-exec.c
 BSD user
 S: Orphan
 F: bsd-user/
+F: default-configs/*-bsd-user.mak
 
 Linux user
 M: Riku Voipio <riku.voipio@iki.fi>
 S: Maintained
 F: linux-user/
+F: default-configs/*-linux-user.mak
 
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