powerpc/pseries: drop RTAS-based timebase synchronization

The pseries platform has been LPAR-only for several generations, and
the PAPR spec:

* Guarantees that timebase synchronization is performed by
  the platform ("The timebase registers are synchronized by the
  platform before CPUs are given to the OS" - 7.3.8 SMP Support).

* Completely omits the RTAS freeze-time-base and thaw-time-base RTAS
  functions, which are CHRP artifacts.

This code is effectively unused on currently supported models, so drop
it.
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230125-b4-powerpc-rtas-queue-v3-7-26929c8cce78@linux.ibm.com

arch/powerpc/platforms/pseries/smp.c

@@ -278,11 +278,5 @@ void __init smp_init_pseries(void)
 		cpumask_clear_cpu(boot_cpuid, of_spin_mask);
 	}
 
-	/* Non-lpar has additional take/give timebase */
-	if (rtas_token("freeze-time-base") != RTAS_UNKNOWN_SERVICE) {
-		smp_ops->give_timebase = rtas_give_timebase;
-		smp_ops->take_timebase = rtas_take_timebase;
-	}
-
 	pr_debug(" <- smp_init_pSeries()\n");
 }