RX-51: Add support for OMAP3 ROM Random Number Generator

Adding this driver as platform device and only for RX-51 until somebody test if
it working also on other OMAP3 HS devices and until there will be generic ARM
way to deal with SMC calls.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
[tony@atomide.com: folded in the clock alias change]
Signed-off-by: Tony Lindgren <tony@atomide.com>