Change the dev name from PWM to PWM_0. This will make it
consistent with other drivers and also fix the device binding
failure in the PWM sample app.
Jira: ZEP-395
Change-Id: I90b945a7e57700d384eaa52e5300c881a3251d83
Signed-off-by: Baohong Liu <baohong.liu@intel.com>