Don't clear interrupts on disabling, because
* Sun4M_SystemArchitecture_edited2.pdf doesn't describe
  that masking or un-masking IRQ shall clear pending ones.

* Field tests also show that SPARCstation-20 doesn't
  clear them.

* The patch makes Solaris 2.5.1/2.6 boot ~1500 times
  faster (~20 seconds instead of ~8 hours)
Signed-off-by: NArtyom Tarasenko <atar4qemu@gmail.com>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>