MIPS: Alchemy: Remove dead CONFIG_SOC_AU1000_FREQUENCY

CONFIG_SOC_AU1000_FREQUENCY doesn't exist in Kconfig, therefore
removing all references for it from the source code.

Signed-off-by: Christoph Egger <siccegge@cs.fau.de>
To: linux-mips@linux-mips.org
To: linux-kernel@vger.kernel.org
Cc: vamos@i4.informatik.uni-erlangen.de
Patchwork: https://patchwork.linux-mips.org/patch/1367/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>