PCI: endpoint: Add missing documentation about the MSI/MSI-X range

Both pci_epc_raise_irq() and pci_epc_map_msi_irq() APIs expect the
MSI/MSI-X vectors to start from 1 but it is not documented. Add the range
info to the kdoc of the APIs to make it clear.

Link: https://lore.kernel.org/r/20230602114756.36586-2-manivannan.sadhasivam@linaro.org
Fixes: 5e8cb40 ("PCI: endpoint: Add EP core layer to enable EP controller and EP functions")
Fixes: 87d5972 ("PCI: endpoint: Add pci_epc_ops to map MSI IRQ")
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

Author: Mani-Sadhasivam

drivers/pci/endpoint/pci-epc-core.c

@@ -213,7 +213,7 @@ EXPORT_SYMBOL_GPL(pci_epc_start);
  * @func_no: the physical endpoint function number in the EPC device
  * @vfunc_no: the virtual endpoint function number in the physical function
  * @type: specify the type of interrupt; legacy, MSI or MSI-X
- * @interrupt_num: the MSI or MSI-X interrupt number
+ * @interrupt_num: the MSI or MSI-X interrupt number with range (1-N)
  *
  * Invoke to raise an legacy, MSI or MSI-X interrupt
  */
@@ -246,7 +246,7 @@ EXPORT_SYMBOL_GPL(pci_epc_raise_irq);
  * @func_no: the physical endpoint function number in the EPC device
  * @vfunc_no: the virtual endpoint function number in the physical function
  * @phys_addr: the physical address of the outbound region
- * @interrupt_num: the MSI interrupt number
+ * @interrupt_num: the MSI interrupt number with range (1-N)
  * @entry_size: Size of Outbound address region for each interrupt
  * @msi_data: the data that should be written in order to raise MSI interrupt
  *            with interrupt number as 'interrupt num'