target/arm: Convert VCMLA, VCADD size field to MO_* in decode

target/arm: Convert VCMLA, VCADD size field to MO_* in decode

The VCMLA and VCADD insns have a size field which is 0 for fp16
and 1 for fp32 (note that this is the reverse of the Neon 3-same
encoding!). Convert it to MO_* values in decode for consistency.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200903133209.5141-4-peter.maydell@linaro.org