[BBT#199] Add an Open MP target device

[abouteiller]

This is a transfer of https://bitbucket.org/icldistcomp/parsec/pull-requests/199

• Rename gpu_* in device_cuda.[ch]
• Add a core dgemm that executes on hosted MIC with OpenMP target
• Add an OpenMP target body to LLT
• Configury to make it compile in target mode with icc

How to try/use:

Compile PaRSEC using either

• Intel ICC 17.xx (not 18.xx) with MPSS 3.8 → executes on KNC Mic
• gcc > 7.3 with the Open ACC PTX enabled → executes on Nvidia
• gcc > 7.3 with the Mic emulation device enabled → executes on Host in Mic emulation mode