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-lm32/helper.c b/target-lm32/helper.c
index 47ae7e7..a0a8399 100644
--- a/target-lm32/helper.c
+++ b/target-lm32/helper.c
@@ -42,8 +42,11 @@
     return addr & TARGET_PAGE_MASK;
 }
 
-void do_interrupt(CPULM32State *env)
+void lm32_cpu_do_interrupt(CPUState *cs)
 {
+    LM32CPU *cpu = LM32_CPU(cs);
+    CPULM32State *env = &cpu->env;
+
     qemu_log_mask(CPU_LOG_INT,
             "exception at pc=%x type=%x\n", env->pc, env->exception_index);