Changed deprecation warning for Data#toBits to recommend asUInt instead...

Changed deprecation warning for Data#toBits to recommend asUInt instead because the sole remaining use of toBits in chiselTests was to compare to Vectors declared differently but with same underlying bits.
Making at toBits was problematic because it did not support === method.
Changed Vec and Bundle to both support toUInt()
Note: If toBits is actually needed now, one can use toInt().toBits()