ARM: dts: s3c64xx: Enable PWM node by default

The PWM block is required for system clock source so it must be always
enabled. This patch fixes boot issues on SMDK6410 which did not have the
node enabled explicitly for other purposes.

Fixes: eeb93d02c5d8 ("clocksource: of: Respect device tree node status")
Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>