doc: Align terminal client usage for Arm platforms

For both Corstone-1000 and N1SDP, show examples for picocom but make it
clear any terminal client should work fine (giving picocom, minicom, and
screen as examples).

Remove the statement about port names being different on Windows as the
rest of the documentation just assumes a Linux host is being used.

Signed-off-by: Adam Johnston <adam.johnston@arm.com>