AR: Comment itrigger limited to 32 ints if XLEN=32

[timsifive]

Resolves #904.

[pdonahue-ventana]

I don't think that the priv spec reserves 32-47. I think that it's AIA that does so. The priv spec says that >= 16 are designated for platform use (both in table 3.6 and table 9.6).

[timsifive]

You're right. I must have been looking at the exceptions when I wrote that.

So this is another in-future-versions-of-the-spec thing. Getting really tired of updating our spec to work with a document that doesn't even exist in draft form.

[pdonahue-ventana]

Parser error: "a trigger interrupts" doesn't seem right to me. Maybe this?

Suggested change

	If XLEN is 32, then it is not possible to set a trigger interrupts with
	Exception Code larger than 31. A future version of the RISC-V Privileged
	If XLEN is 32, then it is not possible to set a trigger for interrupts with
	Exception Code larger than 31. A future version of the RISC-V Privileged

[timsifive]

Fixed. Thanks.