i965: Expose write_reg() as brw_store_register_mem64().

i965: Expose write_reg() as brw_store_register_mem64().

Writing a 64-bit register value to memory is sufficiently complicated
that it makes sense to reuse this function rather than duplicating it.

Exposing it outside of gen6_queryobj.c means it needs a more descriptive
function name.  It could probably be moved to brw_util.c or somewhere
else, but this works too.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>