omap443x_cpu_control: Rename def_ft to mpu_def_ft

In preparation for a gpu_def_ft
omap443x_cpu_control: Do not change the dependent voltage

See arch/arm/mach-omap2/opp4xxx_data.c,
"Dependency of domains are as follows for OMAP4430 (OPP based):"

There is no reason to go above OPP100 on the dependent voltage (that's
the core voltage). Hence, do not change those dependent voltages.
omap4430_cpu_control: Introduce GPU freq control