ARM - OMAP: ads7846: fix pendown debounce setting

Commit 97ee9f01 (ARM: OMAP: fix the ads7846 init code) have enabled the
pendown GPIO debounce time setting by the below sequence:

  gpio_request_one()
  gpio_set_debounce()
  gpio_free()

It also revealed a bug in the OMAP GPIO handling code which prevented
the GPIO debounce clock to be disabled and CORE transition to low power
states.

Commit c9c55d92 (gpio/omap: fix off-mode bug: clear debounce settings on
free/reset) fixes the OMAP GPIO handling code by making sure that the
GPIO debounce clock gets disabled if no GPIO is requested from current
bank.

While fixing the OMAP GPIO handling code (in the right way), the above
commit makes the gpio_request->set_debounce->free sequence invalid as
after freeing the GPIO, the debounce settings are lost.

Fix the debounce settings by moving the debounce initialization to the
actual GPIO requesting code - the ads7846 driver.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>