dm: Select CONFIG_SPL_GPIO_SUPPORT on OMAP

This fixes the breakage with SPL on most OMAP boards after the GPIO
driver was moved.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: U-Boot DM <u-boot-dm@lists.denx.de>
Cc: Tom Rini <trini@ti.com>
Acked-by: Tom Rini <trini@ti.com>
Signed-off-by: Tom Rini <trini@ti.com>