isci: cleanup silicon revision detection

Perform checking per-pci device (even though all systems will only have
1 pci device in this generation), and delete support for silicon that
does not report a proper revision (i.e. A0).

Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/scsi/isci/phy.c b/drivers/scsi/isci/phy.c
index e56080a..d8f893e 100644
--- a/drivers/scsi/isci/phy.c
+++ b/drivers/scsi/isci/phy.c
@@ -211,7 +211,7 @@
 	llctl |= SCU_SAS_LLCTL_GEN_VAL(MAX_LINK_RATE, link_rate);
 	writel(llctl, &iphy->link_layer_registers->link_layer_control);
 
-	if (is_a0() || is_a2()) {
+	if (is_a2(ihost->pdev)) {
 		/* Program the max ARB time for the PHY to 700us so we inter-operate with
 		 * the PMC expander which shuts down PHYs if the expander PHY generates too
 		 * many breaks.  This time value will guarantee that the initiator PHY will