[MLIR][OpenMP][Flang] Set OpenMP target attributes in MLIR module

Scope of changes:
  1) Add attribute to OpenMP MLIR dialect which stores target cpu and
     target features
  2) Store target information in MLIR module

Differential Revision: https://reviews.llvm.org/D146612



Reviewed By: kiranchandramohan

Co-authored-by: Kiran Chandramohan <kiran.chandramohan@arm.com>