MIPS: Alchemy: remove SOC_AU1X00 in favor of MIPS_ALCHEMY

Remove the CONFIG_SOC_AU1X00 Kconfig symbol since its job can also be done
by MACH_ALCHEMY, now renamed to MIPS_ALCHEMY.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
To: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/1461/


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