ARM: OMAP3530evm: set pendown_state and debounce time for ads7846

Currently most ads7846 config definitions for OMAP3 series boards have
been moved to common-board-devices.c, and it is transparent for init.
And it's no very proper to do gpio_request based on get_pendown_state
since omap_ads7846_init knows everything about ads7846_config.

So it's more fit to request gpio according to the right gpio_pendown
and set debounce time conditionally. If we don't set proper debouce
time, there are flooded interrupt counters of ads7846 responding to
one time touch on screen, then the driver couldn't work very well.

This patch has been validated on 3530evm.

Signed-off-by: Zumeng Chen <zumeng.chen@windriver.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>