KVM: arm64: Emulate SPE buffer management interrupt

A profiling buffer management interrupt is asserted when the buffer fills,
on a fault or on an external abort. The service bit, PMBSR_EL1.S, is set as
long as SPE asserts this interrupt. The interrupt can also be asserted
following a direct write to PMBSR_EL1 that sets the bit. The SPE hardware
stops asserting the interrupt only when the service bit is cleared.

KVM emulates the interrupt by reading the value of the service bit on
each guest exit to determine if the SPE hardware asserted the interrupt
(for example, if the buffer was full). Writes to the buffer registers are
trapped, to determine when the interrupt should be cleared or when the
guest wants to explicitely assert the interrupt by setting the service bit.