i965: Drop alignment parameter from bo_alloc_internal().

i965: Drop alignment parameter from bo_alloc_internal().

Buffers are always page aligned on 965+ hardware; I believe this extra
parameter is a vestige from the Gen2-3 era.

All callers pass 0, and in fact we assert that the alignment is 0 unless
BO_ALLOC_BUSY is set (for some reason).  We can just drop the parameter
and set the value to 0 explicitly.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>