[flang][openacc] Fix device_num and device_type clauses for init directive

This patch fix the device_num and device_type clauses used in the init clause. device_num was not
spelled correctly in the parser and was to restrictive with scalarIntConstantExpr instead of scalarIntExpr.
device_type is now taking a list of ScalarIntExpr.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D88571