sata_mv: move SOC_FLAG to hpriv

Convert the System-on-Chip flag from a host flag to an hpriv flag,
for better consistency with other chip-rev flags, and for easier use
in errata fixes etc.

Also change the related "HAS_PCI()" into "!IS_SOC()" for better consistency
of naming/use (everything else SOC-related already uses "SOC").

There are no functionality changes in this patch.

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