misc: pci_endpoint_test: Enable/Disable MSI using module param

In certain platforms like TI's DRA7 SoCs, use of legacy PCI interrupt is
exclusive with use of MSI (Section 24.9.4.6.2.1 Legacy PCI Interrupts in
http://www.ti.com/lit/ug/spruhz6i/spruhz6i.pdf

).

However pci_endpoint_test driver enables MSI by default in probe.  In order
for pci_endpoint_test to be able to test legacy interrupt, MSI should be
disabled. Add a module param 'no_msi' to disable MSI (only when legacy
interrupt has to be tested).

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
[bhelgaas: folded in static fix from Colin Ian King <colin.king@canonical.com>]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>