ARM: davinci_all_defconfig: enable LED default-on trigger

The LEDs default-on trigger is nice to have. For example, it can be used
to configure a LED as a power indicator.

Signed-off-by: David Lechner <david@lechnology.com>
[nsekhar@ti.com: build as module, subject line fixes]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>