ir_to_mesa: Implement ir_binop_all_equal using DP4 w/SGE

The operation ir_binop_all_equal is !(a.x != b.x || a.y != b.y || a.z
!= b.z || a.w != b.w).  Logical-or is implemented using addition
(followed by clampling to [0,1]) on values of 0.0 and 1.0.  Replacing
the logical-or operators with addition gives !bool((int(a.x != b.x) +
int(a.y == b.y) + int(a.z == b.z) + int(a.w == b.w)).  This can be
implemented using a dot-product with a vector of all 1.0.  After the
dot-product, the value will be an integer on the range [0,4].

Previously a SEQ instruction was used to clamp the resulting logic
value to [0,1] and invert the result.  Using an SGE instruction on the
negation of the dot-product result has the same effect.  Many older
shader architectures do not support the SEQ instruction.  It must be
emulated using two SGE instructions and a MUL.  On these
architectures, the single SGE saves two instructions.

Reviewed-by: Eric Anholt <[email protected]>

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