logging: Handle nios2 global pointer register issue

Nios2 is trying to use global pointer register to access variables
smaller than 8 bytes. GPR range is limited to 64 bytes and apparently
does not handle well variables placed in custom sections.

Current workaround is to increase logger structures (const and dynamic)
size (+8 bytes for dynamic, +4 bytes for constant). Then GPR is not
used and application can be linked. The downside is increase of memory
usage:
- ROM: <num_of_log_modules>*4 bytes
- RAM: <num_of_log_modules>*8 bytes (if runtime filtering is enabled)

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>