s390/setup: cleanup machine flags

Over time some machine flags got unused (e.g. MACHINE_FLAG_MVPG)
or are available on all 64bit systems (MACHINE_FLAG_CSP,
MACHINE_FLAG_IEEE) - let's remove them.
Reorder the other ones to match the order of the MACHINE_HAS_*
macros and renumber all bits to avoid holes.
Also fix the comment about where the flags are detected.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>