target-arm: Correct misleading 'is_thumb' syn_* parameter names

target-arm: Correct misleading 'is_thumb' syn_* parameter names

In syndrome register values, the IL bit indicates the instruction
length, and is 1 for 4-byte instructions and 0 for 2-byte
instructions. All A64 and A32 instructions are 4-byte, but
Thumb instructions may be either 2 or 4 bytes long. Unfortunately
we named the parameter to the syn_* functions for constructing
syndromes "is_thumb", which falsely implies that it should be
set for all Thumb instructions, rather than only the 16-bit ones.
Fix the functions to name the parameter 'is_16bit' instead.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Sergey Fedorov <serge.fdrv@gmail.com>
Message-id: 1454683067-16001-2-git-send-email-peter.maydell@linaro.org