ARM: OMAP2+: Cleanup omap_gpio_dev_attr usage

The omap_gpio_dev_attr data was used to supply instance-specific
data for legacy non-DT devices. The GPIO legacy device support has
been cleaned up in commit 14944934

 ("ARM: OMAP2+: Remove legacy
gpio code") a while ago and this data is therefore no longer needed.
So, cleanup the structure and all the associated data in various
hwmod data files.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>