md-new-param-to_sync_page_io

md-new-param-to_sync_page_io

Add new parameter to 'sync_page_io'.

The new parameter allows us to distinguish between metadata and data
operations.  This becomes important later when we add the ability to
use separate devices for data and metadata.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>