Copyright and License header put in most files

A further check is needed, but now all files have their Copyright + License
header.

Signed-off-by: Aurelio Colosimo <aurelio@aureliocolosimo.it>
trivial arch-atmega/pwm.c: do not define NPWM, use ARRAY_SIZE instead

Signed-off-by: Aurelio Colosimo <aurelio@aureliocolosimo.it>
pwm: rewrite common code in parametrized functions, when possible

This patch permits to simplify and reduce flash size of pwm implementation
in arch-atmega, by putting in the same function the commands for enable/disable,
polarity, duty_cycle.

Signed-off-by: Aurelio Colosimo <aurelio@aureliocolosimo.it>
arch-atmega pwm: at disable, don't set 'in' dir if gpio was out before enable

Signed-off-by: Aurelio Colosimo <aurelio@aureliocolosimo.it>