i965: Always use the pre-computed offset for the relocation entry

i965: Always use the pre-computed offset for the relocation entry

We must be careful to only compute the address once based on the
per-context information (rather than accessing the unlocked global
bo->offset64) so that the value in the batch does match the
reloc.presumed_offset we declare to the kernel. Otherwise, highly
unlikely, but we may see GPU hangs in multithreaded users.

The only real complication here is isl_surf_fill_state() which needs to
adjust the reloc.delta to both general a tile offset and to encode state
into the lower 12 bits.

(Rebased on ISL changes by Ken.)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>