logging: fix format strings not being put in log_strings_area

Commit caea9dc1
("logging: Use TYPE_SECTION macros for log strings") changed to
use TYPE_SECTION macros for log strings. However, the data type
was changed from char[] to (char *), resulting in the pointer
to log strings are being put in the log_strings_area section
instead of the actual strings. Fix this by reverting the data
type change back to before that commit but semantically uses
TYPE_SECTION_ITERABLE() by expanding it manually.

Fixes #58476

Signed-off-by: Daniel Leung <daniel.leung@intel.com>