ACPI/PCI: PCI MSI _OSC support capabilities called when root bridge added

The _OSC capability OSC_MSI_SUPPORT is set when the root bridge is added
with pci_acpi_osc_support(), so we no longer need to do it in the PCI
MSI driver.  Also adds the function pci_msi_enabled, which returns true
if pci=nomsi is not on the kernel command-line.

Signed-off-by: Andrew Patterson <andrew.patterson@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index 9fe026b..5b38a02 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -350,6 +350,8 @@
 	if (pcie_aspm_enabled())
 		flags |= OSC_ACTIVE_STATE_PWR_SUPPORT |
 			OSC_CLOCK_PWR_CAPABILITY_SUPPORT;
+	if (pci_msi_enabled())
+		flags |= OSC_MSI_SUPPORT;
 	if (flags != base_flags)
 		pci_acpi_osc_support(device->handle, flags);