ARM: OMAP2+: omap2plus_defconfig: Add tps65217 support

TPS65217 is described in arch/arm/boot/dts/am335x-bone.dts
but doesn't enabled in arch/arm/configs/omap2plus_defconfig.

Enable TPS65217 support in omap2plus_defconfig.

Signed-off-by: Igor Mazanov <i.mazanov@gmail.com>
Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>