GBE: Fixed a bug and release 2 or 3 simdWidth register space.

GBE: Fixed a bug and release 2 or 3 simdWidth register space.

This patch fix two issues. One is for the sel_cmp pattern matching.
We should not set the sel_cmp instruction state to physicalFlag, as
sel_cmp will never use a flag register. And as it set the physicalFlag
and leave the flagIndex to zero. Then it just increase the virtual
register 0's interval to as long as the last sel_cmp instruction,
thus the virtual register 0 will never be freed.

Another issue is that when we allocate special registers. We
are not always allocate them on demand. For example, the 3
local id registers are always allocated. Thus maybe some of the
registers are not used at all. So the interval's end point will
not get a chance to set to a proper value and it will never be
released. Now just init the end point to 0. And latter, if it's
used, it will be set to a proper value. Otherwise, it will be zero,
and will be deallocated when do expiering.

This patch could fix(work around) a long standing bug:
When disable the pre allocation instruction scheduling by
export OCL_PRE_ALLOC_INSN_SCHEDULE=0
And run the case:
utests/utest_run compiler_menger_sponge_no_shadow
it fails.

I spent almost one day to track down that it's related to the register
allocation. But I haven't root caused that where is the actual buggy
code. I doubt the register allocation, but I reviewed the code very
careful, and haven't found anything wrong. Now the last suspect is
in the register interval handling.

Anyway, by apply these patch to release two registers to the pool
which may change the register allocation/expieration, thus work around
that bug. We may still need to spend some time to investigate the root
cause the failure in the future.

Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>
Reviewed-by: "Song, Ruiling" <ruiling.song@intel.com>