cpu: Replace do_interrupt() by CPUClass::do_interrupt method

This removes a global per-target function and thus takes us one step
closer to compiling multiple targets into one executable.

It will also allow to override the interrupt handling for certain CPU
families.

Signed-off-by: Andreas Färber <afaerber@suse.de>
diff --git a/target-alpha/cpu-qom.h b/target-alpha/cpu-qom.h
index 252bd14..32ee286 100644
--- a/target-alpha/cpu-qom.h
+++ b/target-alpha/cpu-qom.h
@@ -74,4 +74,6 @@
 
 #define ENV_OFFSET offsetof(AlphaCPU, env)
 
+void alpha_cpu_do_interrupt(CPUState *cpu);
+
 #endif