ARM: dts: bcm283x: Fix PWM pin assignment

All RPi 1 and 2 boards used the PWM (audio out) on pin 40 and 45.
So it was easy to define them in bcm2835-rpi.dtsi. Starting with RPi 3
this wont work anymore, because it uses pin 40 and 41. Furthermore the
Zero variants doesn't have audio out.

This patch fixes this pin conflict by moving the PWM node to the board-level.

Change summary:
RPi 3 B:      PWM1 45 -> 41
Zero, Zero W: PWM disabled
all other:    no functional change

Reported-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>