x86: avoid an extern declaration

After the previous patch, we can use the proper
declaration in a common header file.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

target-i386/excp_helper.c

@@ -19,6 +19,7 @@
 
 #include "cpu.h"
 #include "qemu-log.h"
+#include "sysemu.h"
 #include "helper.h"
 
 #if 0
@@ -39,10 +40,6 @@ void helper_raise_exception(CPUX86State *env, int exception_index)
     raise_exception(env, exception_index);
 }
 
-
-/* This should come from sysemu.h - if we could include it here... */
-void qemu_system_reset_request(void);
-
 /*
  * Check nested exceptions and change to double or triple fault if
  * needed. It should only be called, if this is not an interrupt.