s390: Remove GENERIC_LOCKBREAK Kconfig option

s390: Remove GENERIC_LOCKBREAK Kconfig option

s390 selects GENERIC_LOCKBREAK if PREEMPT is enabled. Reason is a historic
18 years old commit [1] which fixed a compile error for PREEMPT enabled
kernels. Back than only PREEMPT_NONE and PREEMPT_VOLUNTARY kernels were
considered to be important for s390. PREEMPT should "just work".

However, since recently PREEMPT is always enabled [2], which also causes
GENERIC_LOCKBREAK to be always enabled. For some workloads this leads to
massive performance degradation; e.g. a simple kernel compile on machines
with many CPUs may take up to four times longer.

To fix this just remove the GENERIC_LOCKBREAK from s390's Kconfig, since
the compile error from 18 years ago does not exist anymore.

[1] commit b6b40c532a36 ("[S390] Define GENERIC_LOCKBREAK.")
[2] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")

Cc: stable@vger.kernel.org
Reported-by: Massimiliano Pellizzer <massimiliano.pellizzer@canonical.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>