target-arm: Update interrupt handling to use target EL

target-arm: Update interrupt handling to use target EL

Updated the interrupt handling to utilize and report through the target EL
exception field.  This includes consolidating and cleaning up code where
needed. Target EL is now calculated once in arm_cpu_exec_interrupt() and
do_interrupt was updated to use the target_el exception field.  The
necessary code from arm_excp_target_el() was merged in where needed and the
function removed.

Signed-off-by: Greg Bellows <greg.bellows@linaro.org>
Acked-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1429722561-12651-4-git-send-email-greg.bellows@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>