Currently LLEXT module starting addresses are hard-coded in their
respective CMakeLists.txt files. This is very wasteful, since it's
unknown in what order modules are loaded, inflexible and not easily
extendible to other platforms. Switch to calculating addresses
automatically based on a single per-platform Kconfig value.
Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>