s390/purgatory: Enforce z10 minimum architecture level

s390/purgatory: Enforce z10 minimum architecture level

The purgatory code is compiled without the -march option. This means the
default architecture level of the compiler is used. This can cause
problems, e.g. if instructions used in inline assemblies are for a higher
architecture level than the default architecture level of the compiler.

Use z10 as minimum architecture level, similar to the boot code, to enforce
a defined architecture level set.

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>