Removed.
Simplification: less env variables, just the one really useful.
Simplified.
Removed __PHIGEMM_CPUONLY, __PHIGEMM_MAGMABLAS, __PHIGEMM_SELFTUNE
Toward a single-gpu phiGEMM... back to the origin (simple code, more
easy to extend and understand)
Massive cleaning, work in progress