[OpenMP] Set RequiresFullRuntime false in SPMDization

SPMDization in D102307 does not change the RequiresFullRuntime argument of kmpc_target_init/deinit calls. However, the constraints of SPMDization detection for converting a target region to SPMD mode should guarantee that the region does not require full runtime support. Hence, this patch sets RequiresFullRuntime to false for improved execution performance.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D105556