i965/fs: double regioning parameters and execsize for DF in IVB/BYT

i965/fs: double regioning parameters and execsize for DF in IVB/BYT

In IVB and BYT, both regioning parameters and execution sizes are measured as
32-bits element size.

So when we have something like:

mov(8) g2<1>DF g3<4,4,1>DF

We are not actually moving 8 doubles (our intention), but 4 doubles.

We need to double the parameters to cope with this issue. However,
horizontal strides don't behave as they're supposed to on IVB
for DF regions, they will cause each 32-bit half of DF sources to be
strided individually, and doubling the value won't make any difference.

v2:
- Use devinfo directly (Matt).
- Use Baytrail instead of Valleview (Matt).
- Use IvyBridge instead of Ivy (Matt)
- Double the exec_size in code emission (Curro)

v3:
- Change hstride doubling by an assert and fix commit log (Curro).
- Substitute remaining compiler->devinfo by devinfo (Curro).

v4:
- Fix comment (Curro).

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>