tcg/s390x: Check for load-on-condition facility at startup

tcg/s390x: Check for load-on-condition facility at startup

The general-instruction-extension facility was introduced in z196,
which itself was end-of-life in 2021.  In addition, z196 is the
minimum CPU supported by our set of supported operating systems:
RHEL 7 (z196), SLES 12 (z196) and Ubuntu 16.04 (zEC12).

Check for facility number 45, which will be the consilidated check
for several facilities.

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