transceiver: add optional Laurent burst LUT modulation (int16)
Introduce an optional Burst LUT optimization for Laurent-based burst
modulation, enabled via --with-burst-lut.
- Add precomputed Laurent LUT tables (float and int16 I/Q variants)
- Generate LUT at initialization (prepareBurstLUT)
- Use LUT-based modulation for sps=4 when enabled
- Add configure.ac option and USE_BURST_LUT define
This reduces runtime computation by replacing per-burst Laurent
processing with memcpy-based LUT lookups.
Change-Id: I1715c2d33dc55fe1c7be5c6e7259d378ea5e80b2
