ide: add ->tf_load and ->tf_read methods

* Add ->tf_load and ->tf_read methods to ide_hwif_t and set the default
  methods in default_hwif_transport().

* Use ->tf_{load,read} instead o calling ide_tf_{load,read}() directly.

* Make ide_tf_{load,read}() static.

There should be no functional changes caused by this patch.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>