I found a handful of XIP-related bit rot when chasing down a
LKP-reported issue.  They're not really related, aside from all being
XIP-related.  I thought I had an XIP build test, I'll make sure to
add/resurrect one when I get back around to these.

Changes since v1 <20220419194846.18318-1-palmer@rivosinc.com>:
* Defines the mapping functions themselves to have no-op bodies, as
  opposed to wrapping their uses.
* 2-4 are new patches.