[thumb2] lift SMLAxy instructions

[grant-h]

Added IL definitions for Thumb2 SMLABB, SMLABT, SMLATB, and SMLATT instructions. (my binary has over 100 of these)
Added test for SMLABB lifting.,

[CLAassistant]

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[grant-h]

[zznop]

Thank you for the PR. I have a branch that includes lifting expansion for many unimplemented thumb/ARM instructions. In this branch I chose to lift these instructions with intrinsics.

10fb01b6   smlabb  r6, r0, r1, r11

LLIL

r6, flag:q = __smlabb(r0, r1, r11)

MLIL

r6, q_28 = __smlabb(source1: r0_69, source2: r1_6, accumulator: r11_1)

I chose an intrinsic primarily because the decompilation is cleaner. I'm not necessarily opposed to lifting it directly, but in your current implementation the Q flag set doesn't appear to be modeled.

For reference:

if ConditionPassed() then
    EncodingSpecificOperations();
    operand1 = if n_high then R[n]<31:16> else R[n]<15:0>;
    operand2 = if m_high then R[m]<31:16> else R[m]<15:0>;
    result = SInt(operand1) * SInt(operand2) + SInt(R[a]);
    R[d] = result<31:0>;
    if result != SInt(result<31:0>) then  // Signed overflow
        APSR.Q = '1';