arch: Remove the "interrupts.hh" switching header file.

arch: Remove the "interrupts.hh" switching header file.

That switching header is no longer necessary since everything outside
of the ISA can use the BaseInterrupts class.

Change-Id: Ie3ed45c38fec24234ff51fb05ba94f6f3cd02afd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20832
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>