irqtop: improve several more option descriptions, and align them all

irqtop: improve several more option descriptions, and align them all

Keep at least two spaces between option+argument and its description,
while making sure not to go above 80 columns per line.

Also, improve the docstring (there is no need to mention that irqtop
is a utility) and remove the ugly Q from the list of interactive keys.

CC: Joe Jin <joe.jin@oracle.com>
CC: Zhenwei Pi <pizhenwei@bytedance.com>
Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>