MFC: r292943, r292960

• (Ab)use udivx for dividing the u_int pc_cpuid when implementing CPU_ISSET(), CPU_SET() etc. in sparc64 asm. This approach has the benefit of not clobbering %y, allowing to revert r222827 and partially r222828.
• In r222828, CATR() already was changed to use the equivalent of PCPU_GET(cpuid) instead of the MD module ID for KTR_MASK, so belatedly also catch up with KTR_CPU and the C side of ktr(9). Originally, in r203838 CATR() was moved away from directly reading the module ID or equivalent as that became impractical with other CPU types than USI/II supported. With r222828 in place, per-CPU data generally is set up soon enough, though, that employing PCPU things in ktr(9) also for use during early stages works.
• Unfortunately, an exception to the latter is the ktr(9) use in pmap_bootstrap(), which actually is run so early that even checking for bootverbose being set via the loader doesn't work. Consequently, replace the ktr(9) use in pmap_bootstrap() with OF_printf(9) and put it under #ifdef DIAGNOSTIC instead.