debugobjects: Don't call fill_pool() in early boot hardirq context

In the Linux kernel, the following vulnerability has been resolved:

debugobjects: Don't call fill_pool() in early boot hardirq context

When booting a debug PREEMPT_RT kernel on an ARM64 system, a "inconsistent

{HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage" lockdep warning message was

reported to the console.

During early boot, interrupts are enabled before the scheduler is

enabled. In this window (before SYSTEM_SCHEDULING is set) interrupts can

fire and in the hard interrupt context handler attempt to fill the pool

This can lead to a deadlock when the interrupt occurred when the interrupt

hits a region which holds a lock that is required to be taken in the

allocation path.

Add a new can_fill_pool() helper and reorder the exception rule and forbid

this scenario by excluding allocations from hard interrupt context.