OMAP3: PM: Adding smartreflex class3 driver

Smartreflex Class3 implementation continuously monitors
silicon performance  and instructs the Voltage Processors
to increase or decrease the voltage.
This patch adds smartreflex class 3 driver. This driver hooks
up with the generic smartreflex driver smartreflex.c to abstract
out class specific implementations out of the generic driver.

Class3 driver is chosen as the default class driver for smartreflex.
If any other class driver needs to be implemented, the init of that
driver should be called from the board file. That way the new class driver
will over-ride the Class3 driver.

Signed-off-by: Thara Gopinath <thara@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>