ppc64/aarch64: Export __page_{shift, size} in libcompel

Libcompel supplies to the parasite PAGE_SIZE during infection.
On ppc64/aarch64 PAGE_SIZE can be different with Large pages,
under the cover it returns __page_size.

At this moment __page_size is located in criu binary, which
prevents using libcompel as .so library in other applications
than criu on ppc64/aarch64.

Export __page_size and __page_shift in libcompel.

Fixes: #572
Fixes: 2d965008 ("ppc64/aarch64: Dynamically define PAGE_SIZE")

Cc: Adrian Reber <areber@redhat.com>
Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reported-by: Alexey Shabalin
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>