MIPS: Alchemy: get rid of allow_au1k_wait

Eliminate the 'allow_au1k_wait' variable.  MIPS kernel installs the
Alchemy-specific wait code before timer initialization;  if the C0
timer must be used for timekeeping the wait function is set to NULL
which means no wait implementation is available.

As a sideeffect, the 'wait instruction available' output in
/proc/cpuinfo now correctly indicates whether 'wait' is usable.

Run-tested on DB1200.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>