Enhance GenArrayGet, GenArrayPut for x86

As pointed out by Ian Rogers, the x86 versions didn't optimize
handling of constant index expressions.  Added that support,
simplified checking of constant indices, and removed the use of
a temporary register for the 'wide' cases by using x86 scaled
addressing mode.

Change-Id: I82174e4e3674752d00d7c4730496f59d69f5f173
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>
3 files changed