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-xtensa/helper.c b/target-xtensa/helper.c
index a8a6493..6f613c66 100644
--- a/target-xtensa/helper.c
+++ b/target-xtensa/helper.c
@@ -178,8 +178,11 @@
     }
 }
 
-void do_interrupt(CPUXtensaState *env)
+void xtensa_cpu_do_interrupt(CPUState *cs)
 {
+    XtensaCPU *cpu = XTENSA_CPU(cs);
+    CPUXtensaState *env = &cpu->env;
+
     if (env->exception_index == EXC_IRQ) {
         qemu_log_mask(CPU_LOG_INT,
                 "%s(EXC_IRQ) level = %d, cintlevel = %d, "