target-arm: Split data abort syndrome generator

Split the data abort syndrome generator into two versions:
One with a valid Instruction Specific Syndrome (ISS) and another without.

The following new flags are supported by the syndrome generator
with ISS:
* isv - Instruction syndrome valid
* sas - Syndrome access size
* sse - Syndrome sign extend
* srt - Syndrome register transfer
* sf  - Sixty-Four bit register width
* ar  - Acquire/Release

These flags are not yet used, so this patch has no functional change
except that we will now correctly set the IL bit in data abort
syndromes without ISS information.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1461931684-1867-5-git-send-email-edgar.iglesias@gmail.com>
[PMM: squashed in with patch which was just adding the IL bit]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
