Implement sched_getattr and sched_setattr syscalls decoding

* xlat/sched_flags.in: New file.
* sched.c: Include "xlat/sched_flags.h".
(print_sched_attr, sys_sched_setattr, sys_sched_getattr): New functions.
* linux/dummy.h (sys_sched_getattr, sys_sched_setattr): Remove.
* tests/sched_xetattr.c: New file.
* tests/sched_xetattr.test: New test.
* tests/Makefile.am (check_PROGRAMS): Add sched_xetattr.
(TESTS): Add sched_xetattr.test.
* tests/.gitignore: Add sched_xetattr.
7 files changed