GBE: Implement complete register spill policy.

GBE: Implement complete register spill policy.

This patch implement a complete register spill policy.

When it needs to spill a register, we always choose the
register which is in the spill candate map and has
maximum endpoint. One tricky I used here is to merge both
the register's endpoint value and the register itself
into one single key. Then I can use one map to implement a
descending order map according to its value( the instruction
endpoint value). This patch supports to spill both vectors
or non-vectors.

And I move the scratch memory allocation from
instruction selection to register allocation. We may latter
use the internal interval information to reduce the scratch
memory comsumption.

Another big change is that I don't perform the real
spill on the fly. Instead, I move the real spill to the end of
all register allocation. Then spilling all the registers which
in the spillSet at one pass. This has the following advantage:
1. It only needs to loop over all instructions once.
2. When spilling one instruction, we know all the registers' status.
   Then it's easy to know the correct scratch id for each register.
   Actually, the previous implementation has a bug here.

The last part is to avoid the spill instruction restrication.
As ruiling pointed out that the spill instruction(scratch read/write)
doesn't support predication correctly for non-DW data type.

This patch avoids to spill any non-supported type register.

After this patch, both luxrender and opencv examples work fine on
my machine.

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>
Reviewed-by: Yang, Rong R <rong.r.yang@intel.com>