sata_promise: new EH conversion for 20619 chips, take 2

This patch updates the sata_promise driver to use new-style
libata error handling for 20619 (TX4000) chips. sata_promise
already uses new EH for the other chips it supports, so the
patch is quite simple:

* remove ->phy_reset and ->eng_timeout ops from pdc_pata_ops,
  and instead bind ->freeze, ->thaw, ->error_handler, and
  ->post_internal_cmd to existing new EH functions
* drop ATA_FLAG_SRST from board_20619's flags
* remove now unused pdc_pata_phy_reset() and pdc_eng_timeout()

Tested on a TX4000 with both modern working disks and old/quirky
disks. Also used a CD-RW drive to test reading and writing CDs.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Jeff Garzik <jeff@garzik.org>