sata_mv hardreset rework

Rework and simplify sata_mv's hardreset code to take advantage of
libata improvements since it was first coded.

Also, get rid of the now unnecessary prereset, postreset, and phy_reset
functions.

This patch also paves the way for subsequent pmp support patches,
which will follow once this one passes muster.

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>