i965: Fix ARB_indirect_parameters logic.

This patch modifies the ARB_indirect_parameters logic in
brw_draw_prims, so that our implementation isn't affected if
another application attempts to use predicates. Previously we
were using a predicate with a DELTAS_EQUAL comparison operation
and relying on the MI_PREDICATE_DATA register being 0. Our code
to initialize MI_PREDICATE_DATA to 0 was incorrect, so we were
accidentally using whatever value was written there. Because the
kernel does not initialize the MI_PREDICATE_DATA register on
hardware context creation, we might inherit the value from whatever
context was last running on the GPU (likely another process).
The Haswell command parser also does not currently allow us to write
the MI_PREDICATE_DATA register. Rather than fixing this and requiring
an updated kernel, we switch to a different approach which uses a
SRCS_EQUAL predicate that makes no assumptions about the states of any
of the predicate registers.

Fixes Piglit's spec/arb_indirect_parameters/tf-count-arrays test.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103085
Signed-off-by: Plamena Manolova <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>

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