[OpenMP][CUDA] Fix the issue that P2P memcpy doesn't work

This patch fixes the issue that P2P memcpy doesn't work. The root cause is we didn't set current context when calling the API function. In addition, a matrix to track the states of each pair of devices is also added such that we only need to query and configure the device once.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D122764