arch,cpu,mem: Replace the mmmapped IPR mechanism with local accesses.

The new local access mechanism installs a callback in the request which
implements what the mmapped IPR was doing. That avoids having to have
stubs in ISAs that don't have mmapped IPRs, avoids having to encode
what to do to communicate from the TLB and the mmapped IPR functions,
and gets rid of another global ISA interface function and header files.

Jira Issue: https://gem5.atlassian.net/browse/GEM5-187

Change-Id: I772c2ae2ca3830a4486919ce9804560c0f2d596a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23188
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/SConscript

@@ -63,7 +63,6 @@ env.SwitchingHeaders(
         kernel_stats.hh
         locked_mem.hh
         microcode_rom.hh
-        mmapped_ipr.hh
         process.hh
         pseudo_inst.hh
         registers.hh