taprio: Add support for cycle_time and cycle_time_extension

taprio: Add support for cycle_time and cycle_time_extension

This allows a cycle-time and a cycle-time-extension to be specified.

Specifying a cycle-time will truncate that cycle, so when that instant
is reached, the cycle will start from its beginning.

A cycle-time-extension may cause the last entry of a cycle, just
before the start of a new schedule (the base-time of the "admin"
schedule) to be extended by at maximum "cycle-time-extension"
nanoseconds. The idea of this feauture, as described by the IEEE
802.1Q, is too avoid too narrow gate states.

Example:

tc qdisc change dev IFACE parent root handle 100 taprio \
	      sched-entry S 0x1 1000000 \
	      sched-entry S 0x0 2000000 \
	      sched-entry S 0x1 3000000 \
	      sched-entry S 0x0 4000000 \
	      cycle-time-extension 100000 \
	      cycle-time 9000000 \
	      base-time 12345678900000000

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: David Ahern <dsahern@gmail.com>