i965: Flip arguments to load_register_reg helpers.

i965: Flip arguments to load_register_reg helpers.

load_register_imm and load_register_mem take the destination as the
first argument, so I'd like load_register_reg to do the same the sake
of consistency.  Otherwise, reading sequences of mixed LRI/LRM/LRR is
needlessly confusing.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>