hexagon: add GGML_HEXAGON_VTCM_SIZE (#31221)
* hexagon: add GGML_HEXAGON_VTCM_MB and GGML_HEXAGON_NTHREADS caps
Change-Id: Idffe1613c8db6f96aa842d43d1b2efaed45462a8
* hexagon: rename VTCM cap to GGML_HEXAGON_VTCM_SIZE, drop NTHREADS cap
Change-Id: If4c5b9ce9fd6b725c3561421c2295d40599d012d
* hexagon: make GGML_HEXAGON_VTCM_SIZE an override, accept K/M/G suffixes
Change-Id: Ib8eea84c22f24e6d986b37f215e504b046478c2c
