Remove arm's cpuconf.h, and references to it, after moving a few lines from
it into pmap-v4.h where they are used. Other than those few lines of
support for different MMU types, nothing in cpuconf.h has been used in our
code for quite a while.

The file existed to set up a variety of symbols to describe the
architecture. Over the past few years we have converted all of our source
to use the new architecture symbols standardized by ARM Inc, and predefined
by both clang and gcc.

PR: 216104