x86, setup: move 32-bit code to .text32

Impact: cleanup

The setup code is mostly 16-bit code, but there is a small stub of
32-bit code at the end.  Move the 32-bit code to a separate segment,
.text32, to avoid scrambling the disassembly.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>