soc/intel_adsp: Build bootloader with Zephyr

The presence of a separate build for the bootloader code has always
been a wart with this platform.  Sharing of code between the two has
required great care. We've had bugs with mismatched include paths,
macro definitions and compiler flags, etc...  And of course it's not
possible for one to see the other; in theory we'd like the ability to
call back into IMR code after startup, to use the space for temporary
storage, etc...

So let's finally do it.  This really isn't that complicated when you
see it in isolation:

+ Move the module manifest metadata into an "rimage_modules.c", and
  put them in their own NOLOAD section where we can grab them later
  with objcopy.

+ Make a new "imr" memory region in the main linker and just paste the
  bootloader linkage (which is now using its own specific sections) in
  there.

+ After zephyr.elf is built and cache-remapped, we can extract the imr
  sections and the appropriate manifest for the bootloader rimage
  module, and then do the converse by excluding them for the main
  image module.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>