1. Regalloc dump output was displaying status updates for the wrong variable in some cases.

2. getPhysicalRegister() creates a variable for referring to a specific physical register for low-level purposes, such as the stack pointer, or the frame pointer, or a pushed/popped callee-save register.  We change its behavior so that all such physical registers do not have their liveness tracked/validated, not just the stack pointer.

For #2, the original behavior was causing a liveness validation failure if a function had a single basic block and used callee-save registers, and the -asm-verbose flag was used.  This is because -asm-verbose runs a final liveness pass after the prolog/epilog are generated, and the initial callee-save register pushes would make it look like single-basic-block variables are live coming into a basic block, which is a hallmark of a liveness problem.

BUG= none
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1353923004 .