Fix LSRA bug with explicit register temporaries

A temporary with an explicit RegisterLocation, such as ESI on x86 didn't
have the register marked as allocated.  This caused it to not be
saved/restored in the prologue/epilogue, causing problems in the caller
routine, which expected it to be saved.  Found while implementing
https://android-review.googlesource.com/#/c/157522/

.

Change-Id: I22ca2b24c2d21b1c6ab6cfb7dec26cb38034a891
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>