[optimizing] x86: Prefer add over lea if possible

Looking at some generated code, I noticed an lea being used when an add
was sufficient.  Check for that case, and generate the add.

Fixed for x86 and x86_64.

Change-Id: I110304ff0fed8837ada96d34353a293d29022ce5
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>