target/ppc: remove unused interrupts from p8_next_unmasked_interrupt

target/ppc: remove unused interrupts from p8_next_unmasked_interrupt

Remove the following unused interrupts from the POWER8 interrupt masking
method:
- PPC_INTERRUPT_RESET: only raised for 6xx, 7xx, 970, and POWER5p;
- Debug Interrupt: removed in Power ISA v2.07;
- Hypervisor Virtualization: introduced in Power ISA v3.0;
- Critical Input, Watchdog Timer, and Fixed Interval Timer: only defined
  for embedded CPUs;
- Critical Doorbell: processor does not implement the "Embedded.Processor
  Control" category;
- Programmable Interval Timer: 40x-only;
- PPC_INTERRUPT_THERM: only raised for 970 and POWER5p;

Signed-off-by: Matheus Ferst <matheus.ferst@eldorado.org.br>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Message-Id: <20221011204829.1641124-14-matheus.ferst@eldorado.org.br>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>