include: avoid useless includes of exec/ headers

Headers in include/exec/ are for the deepest innards of QEMU,
they should almost never be included directly.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch_init.c

@@ -40,7 +40,6 @@
 #include "hw/audio/audio.h"
 #include "sysemu/kvm.h"
 #include "migration/migration.h"
-#include "exec/gdbstub.h"
 #include "hw/i386/smbios.h"
 #include "exec/address-spaces.h"
 #include "hw/audio/pcspk.h"