MIPS: PowerTV: Remove support code.

Nobody seems to care about this platform anymore and my attempts to find
somebody willing to provide some tlc for PowerTV have failed so far.

So let's nuke the bloody thing.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/5910/