Add MADV_POPULATE_READ and MADV_POPULATE_WRITE from Linux 5.14 to bits/mman-linux.h

[DJ Delorie]

Joseph Myers <joseph@codesourcery.com> writes:
> +# define MADV_POPULATE_READ 22	/* Populate (prefault) page tables
> +				   readable.  */
> +# define MADV_POPULATE_WRITE 23	/* Populate (prefault) page tables
> +				   writable.  */

Confirmed that these are the correct values across all arch's in the
linux source tree.

Reviewed-by: DJ Delorie <dj@redhat.com>