OMAP3: voltage: rename "mpu" voltagedomain to "mpu_iva"

This voltage domain (a.k.a. VDD1) contains both the MPU and the IVA, so
rename appropriately.

Also fixup any users of the "mpu" name to use "mpu_iva"

Signed-off-by: Kevin Hilman <khilman@ti.com>