misc: pci_endpoint_test: Defer IRQ allocation until ioctl(PCITEST_SET_IRQTYPE)

Commit a402006d ("misc: pci_endpoint_test: Remove global 'irq_type'
and 'no_msi'") changed so that the default IRQ vector requested by
pci_endpoint_test_probe() was no longer the module param 'irq_type', but
instead test->irq_type. test->irq_type is by default IRQ_TYPE_UNDEFINED
(until someone calls ioctl(PCITEST_SET_IRQTYPE)).

However, the commit also changed so that after initializing test->irq_type
to IRQ_TYPE_UNDEFINED, it also overrides it with driver_data->irq_type, if
the PCI device and vendor ID provides driver_data.

This causes a regression for PCI device and vendor IDs that do not provide
driver_data, and the host side pci_endpoint_test_driver driver failed to
probe on such platforms:

  pci-endpoint-test 0001:01:00.0: Invalid IRQ type selected
  pci-endpoint-test 0001:01:00.0: probe with driver pci-endpoint-test failed with error -22

Considering that the pci endpoint selftests and the old pcitest.sh always
call ioctl(PCITEST_SET_IRQTYPE) before performing any test that requires
IRQs, fix the regression by removing the allocation of IRQs in
pci_endpoint_test_probe().  The IRQ allocation will occur when
ioctl(PCITEST_SET_IRQTYPE) is called.

A positive side effect of this is that even if the endpoint controller has
issues with IRQs, the user can do still do all the tests/ioctls() that do
not require working IRQs, e.g. PCITEST_BAR and PCITEST_BARS.

This also means that we can remove the now unused irq_type from
driver_data. The irq_type will always be the one configured by the user
using ioctl(PCITEST_SET_IRQTYPE). (A user that does not know, or care
which irq_type that is used, can use PCITEST_IRQ_TYPE_AUTO. This has
superseded the need for a default irq_type in driver_data.)

[bhelgaas: add probe failure details]
Fixes: a402006d ("misc: pci_endpoint_test: Remove global 'irq_type' and 'no_msi'")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250416142825.336554-2-cassel@kernel.org