PCI_IOC_MAP_BAR ioctl for userspace BAR mapping

[OliverMiyarUgarte]

PCI_IOC_MAP_BAR ioctl for userspace BAR mapping

Added a new ioctl to /dev/pci that allows userspace drivers to map PCI BARs.

What was done:

• Adds struct pciio_bar_map to pciio.h
• Implements PCI_IOC_MAP_BAR handler in pci_usrreq.c

Testing performed:

• Tested with QEMU's edu device
• Mapped BAR0 and read device ID register
• Verified correct size and offset from kernel ranges

What's Next:

• Expose PCI interrupts as events that can be read from a pci(4) (/dev/pciN) device instance, and use that to implement the pci_intr(9) API in userland.
• Devise a scheme for userland allocate and map memory for DMA in order to implement bus_dma(9).

Note: This is a draft PR to get early feedback before adding documentation and final polish. All feedback welcome!

[OliverMiyarUgarte]

Related to: https://wiki.netbsd.org/projects/project/userland_pci/