doc: disable INLINE_SIMPLE_STRUCTS Doxygen option

This option prevents some structures to have missing pages on the
Doxygen HTML output.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
diff --git a/doc/zephyr.doxyfile.in b/doc/zephyr.doxyfile.in
index 3ee6cee..853de35 100644
--- a/doc/zephyr.doxyfile.in
+++ b/doc/zephyr.doxyfile.in
@@ -363,7 +363,7 @@
 # Man pages) or section (for LaTeX and RTF).
 # The default value is: NO.
 
-INLINE_SIMPLE_STRUCTS  = YES
+INLINE_SIMPLE_STRUCTS  = NO
 
 # When TYPEDEF_HIDES_STRUCT tag is enabled, a typedef of a struct, union, or
 # enum is documented as struct, union, or enum with the name of the typedef. So