KVM: riscv: selftests: Allow number of interrupts to be configurable

It is helpful to vary the number of the LCOFI interrupts generated
by the overflow test. Allow additional argument for overflow test
to accommodate that. It can be easily cross-validated with
/proc/interrupts output in the host.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20250303-kvm_pmu_improve-v2-4-41d177e45929@rivosinc.com


Signed-off-by: Anup Patel <anup@brainfault.org>