shell: add PCI shell

Add basic 'lspci' command to list PCI devices. This command can be
enabled with the new Kconfig PCI_SHELL.

Example:

uart:~$ lspci
0:1 8086:7010 class: 0x1, 1, 4, I/O, addrs: 0xC000-0xC00F, IRQ -1

Signed-off-by: Anas Nashif <anas.nashif@intel.com>