ARM: OMAP3: PM: Only access IVA if one exists

prcm_setup_regs() blindly accesses IVA bits
in the PRM and calls omap3_iva_idle() which
does more IVA related register accesses.
Only do this if the IVA hardware actually
exists.

Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>