gpu/radeon: Set flag to indicate broken 64-bit MSI

Some radeon ASICs don't support all 64 address bits of MSIs despite advertising support for 64-bit MSIs in their configuration space.

This breaks on systems such as IBM POWER7/8, where 64-bit MSIs can be assigned with some of the high address bits set.

This makes use of the newly introduced "no_64bit_msi" flag in structure pci_dev to allow the MSI allocation code to fallback to 32-bit MSIs on those adapters.

---

Adding Alex's review tag. Patch to the driver is identical to the reviewed one, I dropped the arch/powerpc hunk rewrote the subject and cset comment.

---
 drivers/gpu/drm/radeon/radeon_irq_kms.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

index 16807af..c74f12d 100644
@@ -202,6 +202,16 @@ static bool radeon_msi_ok(struct radeon_device *rdev)
 	if (rdev->flags & RADEON_IS_AGP)
 		return false;
 
+	/*
+	 * Older chips have a HW limitation, they can only generate 40 bits
+	 * of address for "64-bit" MSIs which breaks on some platforms, notably
+	 * IBM POWER servers, so we limit them
+	 */
+	if (rdev->family < CHIP_BONAIRE) {
+		dev_info(rdev->dev, "radeon: MSI limited to 32-bit\n");
+		rdev->pdev->no_64bit_msi = 1;
+	}
+
 	/* force MSI on */
 	if (radeon_msi == 1)
 		return true;