cifs: Split parse_reparse_point callback to functions: get buffer and parse buffer

Parsing reparse point buffer is generic for all SMB versions and is already
implemented by global function parse_reparse_point().

Getting reparse point buffer from the SMB response is SMB version specific,
so introduce for it a new callback get_reparse_point_buffer.

This functionality split is needed for followup change - getting reparse
point buffer without parsing it.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>