cpu: Move breakpoints field from CPU_COMMON to CPUState

Most targets were using offsetof(CPUFooState, breakpoints) to determine
how much of CPUFooState to clear on reset. Use the next field after
CPU_COMMON instead, if any, or sizeof(CPUFooState) otherwise.

Signed-off-by: Andreas Färber <afaerber@suse.de>
diff --git a/target-mips/cpu.h b/target-mips/cpu.h
index a1d85ef..3ba3229 100644
--- a/target-mips/cpu.h
+++ b/target-mips/cpu.h
@@ -482,6 +482,7 @@
 
     CPU_COMMON
 
+    /* Fields from here on are preserved across CPU reset. */
     CPUMIPSMVPContext *mvp;
 #if !defined(CONFIG_USER_ONLY)
     CPUMIPSTLBContext *tlb;