target-arm: Clean up DISAS_UPDATE usage in AArch32 translation code

AArch32 translation code does not distinguish between DISAS_UPDATE and
DISAS_JUMP. Thus, we cannot use any of them without first updating PC in
CPU state. Furthermore, it is too complicated to update PC in CPU state
before PC gets updated in disas context. So it is hardly possible to
correctly end TB early if is is not likely to be executed before calling
disas_*_insn(), e.g. just after calling breakpoint check helper.

Modify DISAS_UPDATE and DISAS_JUMP usage in AArch32 translation and
apply to them the same semantic as AArch64 translation does:
 - DISAS_UPDATE: update PC in CPU state when finishing translation
 - DISAS_JUMP:   preserve current PC value in CPU state when finishing
                 translation

This patch fixes a bug in AArch32 breakpoint handling: when
check_breakpoints helper does not generate an exception, ending the TB
early with DISAS_UPDATE couldn't update PC in CPU state and execution
hangs.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
Message-id: 1447097859-586-1-git-send-email-serge.fdrv@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>