i965/eu: set DF imm value to the source of DIM

i965/eu: set DF imm value to the source of DIM

According to HSW's PRM, vol02b, the DIM instruction has the following
restriction:

"Restriction : src0 must be immediate. src0 must specify the :f (F, Float)
type encoding but is an immediate 64-bit DF (Double Float) value. dst
must have type DF."

This commit allows to upload the immediate 64-bit DF value to the source
of a DIM instruction even when it is of float type encoding.

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>