ARM: OMAP3: Fix iva2_pwrdm settings for 3703

Commit a819c4f1 (ARM: OMAP3: PM: Only access IVA if one exists)
changed PM to not access IVA registers on omaps that don't have
them. Turns out we still need to idle iva2 as otherwise
iva2_pwrdm will stay on and block deeper idle states.

It seems that the only part of the reset that may not be needed
is the setting of the iva2 boot mode to idle. But as that register
seems to be there and is harmless if no iva2 is on the SoC, it's
probably safest to do the complete reset.

Acked-by: Mark A. Greer <mgreer@animalcreek.com>
Acked-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>