s390/cpumf: remove counter transaction call backs

The command 'perf stat -e cycles ...' triggers the following function
sequence in the CPU Measurement Facility counter device driver:

perf_pmu_event_init()
  __hw_perf_event_init()
    validate_ctr_auth()
    validate_ctr_version()

During event creation, the counter number is checked in functions
validate_ctr_auth() and validate_ctr_version() to verify it is a valid
counter and supported by the hardware. If this is not the case, both
functions return an error and the event is not created. System call
perf_event_open() returns an error in this case.

Later on the event is installed in the kernel event subsystem and the
driver functions cpumf_pmu_add() and cpumf_pmu_commit_txn() are called
to install the counter event by the hardware.

Since both events have been verified at event creation, there is no need
to re-evaluate the authorization state. This can not change since on
 * LPARs the authorization change requires a restart of the LPAR (and
   thus a reboot of the kernel)
 * DPMs can not take resources away, just add them.

Also the sequence of CPU Measurement facility counter device driver
calls is
  cpumf_pmu_start_txn
  cpumf_pmu_add
  cpumf_pmu_start
  cpumf_pmu_commit_txn
for every single event. Which means the condition in cpumf_pmu_add()
is never met and validate_ctr_auth() is never called.

This leaves the counter device driver transaction functions with
just one task:
start_txn: Verify a transaction is not in flight and call
	perf_pmu_disable()
cancel_txn, commit_txn: Verify a transaction is in flight and call
	perf_pmu_enable()

The same functionality is provided by the default transaction handling
functions in kernel/events/core.c. Use those by removing the
counter device driver private call back functions.

Suggested-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>