Support reg_is_vector_simd()

MMX registers are completely separate registers in relation to SSE's XMM registers. The latter were expanded to larger sizes, namely YMM and ZMM.

Often, we want to test whether a register is a SIMD extension register but not an MMX register. This issue relates to providing this functionality, i.e., it checks whether the register is either an XMM, YMM or ZMM.

Looking at the API, I have a hunch that the now deprecated function reg_is_xmm() was intended to provide this requested functionality. In fact, the deprecated function currently checks whether a register is either an XMM or YMM. The name of the function just confuses matters.