pci arbiter: add new --device command line option

[Joan Lledó]

Hello Hurd,

I made some changes in the options parser to add a new --device option, as a
shortcut for current -D -b -d -f options.

I also renamed some options in order to free -D and --device to use it for this
purpose. From now on, the formerly called "devices" are now called "slots", and
"device" will refer to a combination of Domain + Bus + Slot + Function.