Bad page state BUG triggered by init process (kernel 3.1.2)

[Bruce Stenning]

> BUG: Bad page state in process busybox  pfn:00000
> page:c0291000 count:0 mapcount:0 mapping:  (null) index:0x0
> page flags: 0x200(arch_1)

After some experimentation, the diagnostics provided by CONFIG_DMA_API_DEBUG
have shown up problems in the IOP ADMA self-tests (inconsistencies between
map and unmap of DMA pages) and disabling these self-tests removes the
DMA API use warnings and prevents the bad page state bug from triggering
when init runs.

Bruce.