PCI/VGA: Replace full MIT license text with SPDX identifier

Per Documentation/process/license-rules.rst, the SPDX MIT identifier is
equivalent to including the entire MIT license text from
LICENSES/preferred/MIT.

Replace the MIT license text with the equivalent SPDX identifier.

Link: https://lore.kernel.org/r/20220224224753.297579-12-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>