arm: Remove unnecessary includes of hw/arm/arm.h

arm: Remove unnecessary includes of hw/arm/arm.h

The hw/arm/arm.h header now only includes declarations relating
to boot.c code, so it is only needed by Arm board or SoC code.
Remove some unnecessary inclusions of it from target/arm files
and from hw/intc/armv7m_nvic.c.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190516163857.6430-3-peter.maydell@linaro.org