irqtop: use irqtop_puts() for pre-formatted table data

irqtop: use irqtop_puts() for pre-formatted table data

Avoid unnecessary printf formatting when outputting pre-formatted
table strings. The new irqtop_puts() writes data directly via
fputs/waddstr without extra buffer allocation, appending a specified
number of trailing newlines.

This also reduces the buffer size requirements for the vw_printw()
slang fallback, which is now only used for the short header line.

Signed-off-by: Karel Zak <kzak@redhat.com>