i965/blorp: Get rid of brw_context

i965/blorp: Get rid of brw_context

This commit switches all of blorp from taking a brw_context to taking a
blorp_context and, where useful, a void *batch.  In the GL driver, we only
have one active batch at a time so the brw_context *is* the batch but in
Vulkan, batch will point to the anv_cmd_buffer in which we are building
instructions.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>