x86: skip printing args when unwinding stack

On 32-bit x86, it was supposed to print the first argument to
the function during stack trace. However, it only works when
code optimizations are totally disabled (i.e. -O0). As such,
printing the args is not meaningful to aid with debugging.
So change it to simply print the function address, the same
as x86 64-bit.

Also, since unwind_stack() has exactly one caller, make it
ALWAYS_INLINE to skip a function call.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>