tests/tcg/i386: Move smc_code2 to an executable section

We're about to start validating PAGE_EXEC, which means
that we've got to put this code into a section that is
both writable and executable.

Note that this test did not run on hardware beforehand either.

Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Tested-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>