riscv/vdso: don't clear PG_reserved

riscv/vdso: don't clear PG_reserved

The VDSO is part of the kernel image and therefore the struct pages are
marked as reserved during boot.

As we install a special mapping, the actual struct pages will never be
exposed to MM via the page tables.  We can therefore leave the pages
marked as reserved.

Link: http://lkml.kernel.org/r/20190114125903.24845-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Palmer Dabbelt <palmer@sifive.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Tobias Klauser <tklauser@distanz.ch>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>