ARM: davinci: dm646x does not have a DSP domain

Fix the incorrect classification of DSP clock into a
seperate DSP domain on DM646x.

Per the reference guide (http://www.ti.com/lit/ug/spruep9e/spruep9e.pdf

)
there is only one "AlwaysON" power domain on DM6467.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>