GBE: optimize IMM handling for SEL/SEL_CMP/CMP.

GBE: optimize IMM handling for SEL/SEL_CMP/CMP.

Actually, all of the above 3 instructions could avoid
one LOADI instruction by switching operands position.

This patch impemented this optimization. And consolidate
all the same type of optimization into one place.

No obvious performance impact on luxmark.

v2:
fix some wrong indent.
v3:
fix the OP_ORD issue. OP_ORD use both src0/src1 as both src0/src1
so can't use this IMM optimization.

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