lp8727_charger: Add configurable debouce timer

Debounce time is configurable in the platform side. If it is not defined,
the default value is 270ms.

Platform data is msec unit, and this time is converted to jiffies
internally. The workqueue uses this jiffies time in the interrupt
handling. So debounce_jiffies is added in the private data.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>