ARM: dts: imx6*-hummingboard2: remove redundant PWM disables

The PWM nodes are already disabled in the imx6qdl.dtsi, so there
is no need to disable them again in the board DTS.

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>