lib: os: cbprintf: Fix static packaging for sparc

Sparc architecture is strange. Va_list arguments are packed (1 byte
alignment) while unaligned access fails. Added dedicated handling of
Z_CBPRINTF_STORE_ARG which is copying the data word by word.

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