libgomp/openacc.f90 – clean-up public/private attributes

libgomp/openacc.f90 – clean-up public/private attributes

        * config/accel/openacc.f90 (module openacc_kinds): Use 'PUBLIC' to mark
        all symbols as public except for the 'use …, only' imported symbol,
        which is private.
        (module openacc): Default to 'PRIVATE' to exclude openacc_internal; mark
        all symbols from module openacc_kinds as PUBLIC
        * openacc.f90: Add comment with crossref to that file and openmp_lib.h;
        fix comment typo.
        * openacc_lib.h (acc_device_gcn): Add this PARAMETER.

From-SVN: r279456