tracing/fastboot: fix row order in bootgraph.pl

tracing/fastboot: fix row order in bootgraph.pl

When bootgraph.pl parses a file, it gives one row for each initcall's
pid.  But they are displayed in random (perl hash) order.  Let's
sort the pids by the start time of their first initcall instead.

This helps trace module initcalls, where each has a separate pid.
bootgraph.pl will show module initcalls during the initramfs; it may
also be adapted to show subsequent module initcalls.

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Acked-by: Frédéric Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>