arch-x86: Keep all the IOAPIC entries masked at startup.
arch-x86: Keep all the IOAPIC entries masked at startup.

There are two entities setting up the IOAPIC when the simulation is
started, the IOAPIC itsef, and the PC platform object. It's probably not
a good idea (and definitely confusing) to have this initialization
happening in two places.

For now at least, lets make the PC platform object mask the IOAPIC lines
at startup like the IOAPIC is doing. This will help prevent spurious
interrupts from being delivered to the CPU during startup.

Change-Id: I10f455d8e0fca28ddaf772c224a32c1f5f2dd37b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55452
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Reviewed-by: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Maintainer: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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