PCI: endpoint: Make pci_epc_class struct constant

Now that the driver core allows for struct class to be in read-only
memory, we should make all 'class' structures declared at build time
placing them into read-only memory, instead of having to be dynamically
allocated at runtime.

Link: https://lore.kernel.org/linux-pci/2024061011-citable-herbicide-1095@gregkh


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>