exec.h cleanup

Move softmmu_exec.h include directives from target-*/exec.h to
target-*/op_helper.c. Move also various other stuff only used in
op_helper.c there.

Define global env in dyngen-exec.h.

For i386, move wrappers for segment and FPU helpers from user-exec.c
to op_helper.c. Implement raise_exception_err_env() to handle dynamic
CPUState. Move the function declarations to cpu.h since they can be
used outside of op_helper.c context.

LM32, s390x, UniCore32: remove unused cpu_halted(), regs_to_env() and
env_to_regs().

ARM: make raise_exception() static.

Convert
#include "exec.h"
to
#include "cpu.h"
#include "dyngen-exec.h"
and remove now unused target-*/exec.h.

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

target-lm32/op_helper.c

@@ -1,5 +1,6 @@
 #include <assert.h>
-#include "exec.h"
+#include "cpu.h"
+#include "dyngen-exec.h"
 #include "helper.h"
 #include "host-utils.h"