GBE: refine the "scalar" register handling.

GBE: refine the "scalar" register handling.

The scalar register's actual meaning should be uniform register.
A non-uniform register is a varying register. For further
uniform analysis and bool data optimization, this patch
make the uniform as a new register data attribute. We
can set each new created register as an uniform or varying
register.

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