omap: header: remove unused data-type

Remove unused data type omap_gpio_switch_config

Thereby also get rid of following sparse warnings:
arch/arm/plat-omap/include/plat/board.h :121:20:
	warning: dubious bitfield without explicit `signed' or `unsigned'
arch/arm/plat-omap/include/plat/board.h :122:19:
	warning: dubious bitfield without explicit `signed' or `unsigned'
arch/arm/plat-omap/include/plat/board.h :123:24:
	warning: dubious bitfield without explicit `signed' or `unsigned'

Signed-off-by: Vikram Pandita <vikram.pandita@ti.com>
Acked-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>