hw/arm/boot: Rebuild hflags when modifying CPUState at boot

Rebuild hflags when modifying CPUState at boot.

Fixes: e979972a
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Message-id: 20191031040830.18800-2-edgar.iglesias@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>