s390x: lib: add and use macros for control register bits

Add CTL0_* and CTL2_* macros for specific control register bits.

Replace all hardcoded values in the library and in the existing testcases so
that they use the new macros.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20210611140705.553307-2-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>