libqos: Update QGuestAllocator to be opaque

libqos: Update QGuestAllocator to be opaque

To avoid the architecture-specific implementations of the generic qtest
allocator having to know about fields within the allocator, add a
page_size setter method for users or arch specializations to use.
The allocator will assume a default page_size for general use, but it
can always be overridden.

Since this was the last instance of code directly using properties of the
QGuestAllocator object directly, modify the type to be opaque and move
the structure inside of malloc.c.

mlist_new, which was previously exported, is made static local to malloc.c,
as it has no external users.

[Peter Maydell <peter.maydell@linaro.org> reported the following clang
warning:
  tests/libqos/malloc.c:35:3: warning:
  redefinition of typedef 'QGuestAllocator' is a C11 feature
        [-Wtypedef-redefinition]
  } QGuestAllocator;

I converted typedef struct ... QGuestAllocator; to struct ...;
--Stefan]

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Marc Marí <marc.mari.barcelo@gmail.com>
Message-id: 1421698563-6977-7-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>