The number of DWords should be even when doing ring emits as
command sequences require QWord alignment.

There was some discussion about the maximum length of the MI_LRI
command. Quoting Mika

"I did some test with bdw:

"The maximum is 128 writes, resulting the 8 bit length
field of the command being 0xff, thus following the spec.
The 128'th write went through.

"Perhaps the max command length is then less in older gens?

"Perhaps WARN_ON(x > 128) in MI_LOAD_REGISTER_IMM would be in place
but one needs minor tweak to command parser a bit also then.

	#define I915_MAX_WA_REGS 16

keeps us safe for now atleast."

Ville commented that on pre-gen6 the length field seems to be
restricted to 0x3f though. So for all cases we should be ok.

v2: user LRI variant that can write multiple regs in one go (Damien).
We can simply insert one NOP at the end instead of one per register write.

Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: NArun Siluvery <arun.siluvery@linux.intel.com>
Reviewed-by: NDamien Lespiau <damien.lespiau@intel.com>
[danvet: Add a summary of the MI_LRI length discussion.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>