Add PCI device enumeration and configuration utilities

This commit introduces a new PCI library and associated tools for inspecting and modifying PCI configuration space via Linux sysfs. The following changes were made:

- Implemented `pci.c` and `pci.h` for PCI device management, including enumeration, attribute reading, and configuration space access.
- Added `setpci` command-line utility for reading and writing PCI configuration registers, with support for filtering devices by vendor, device, and slot.
- Created manual pages for `setpci` to document its usage and options.
- Developed test scripts for both `lspci` and `setpci` to ensure functionality and correctness of the new features.

These additions enhance the ability to interact with PCI devices, providing a robust framework for device management and configuration.

tests/test_setpci.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+_test_name="setpci"
+. "$(dirname "$0")/harness.sh"
+
+setup_tmpdir
+SETPCI="$VX setpci"
+
+echo "Running setpci tests..."
+
+dev_path="/sys/bus/pci/devices/$(ls /sys/bus/pci/devices | head -n 1)"
+slot="$(basename "$dev_path")"
+short_slot="$(printf '%s' "$slot" | sed 's/^0000://')"
+vendor="$(sed 's/^0x//' "$dev_path/vendor")"
+device="$(sed 's/^0x//' "$dev_path/device")"
+command_reg="$(od -An -tx2 -N2 -j4 "$dev_path/config" | tr -d ' \n')"
+
+$SETPCI --dumpregs > dumpregs.out
+check_grep "VENDOR_ID" dumpregs.out "dumpregs: lists standard names"
+
+out="$($SETPCI -s "$short_slot" VENDOR_ID)"
+check_eq "$out" "$vendor" "read: VENDOR_ID matches sysfs"
+
+out="$($SETPCI -s "$short_slot" DEVICE_ID)"
+check_eq "$out" "$device" "read: DEVICE_ID matches sysfs"
+
+out="$($SETPCI -s "$short_slot" 04.w)"
+check_eq "$out" "$command_reg" "read: numeric register syntax works"
+
+check_exit "dry-run: masked write succeeds" 0 $SETPCI -D -s "$short_slot" COMMAND="$command_reg:ffff"
+after="$($SETPCI -s "$short_slot" COMMAND)"
+check_eq "$after" "$command_reg" "dry-run: command register unchanged"
+
+summary