Remove 32-bit SWARM kernels and supporting code.

[jmallett]

Summary

This follows the lead of other MIPS platforms in removing support for 32-bit kernels running on 64-bit CPUs. In particular, SWARM requires that some registers be accessed as 64-bit quantities, and uses an awkward and incomplete assembly routine to provide those accesses on 32-bit kernels. This removes those hacks, which were exposed as general APIs in the MIPS port but fortunately were not used.

Test Plan

Tested with universe build of all remaining kernels.