ARM: dts: OMAP4460: Add bandgap entry for OMAP4460 devices

Add bandgap devices for OMAP4460 devices.

Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>