doc: fix doxygen handling of __attribute__(x)

The predefined macro list for doxygen processing had a typo error
causing __attribute__(x) to not be handled correctly.

kernel.h was recently updated to include use of
 __attribute__((sentinel)) and doxygen wasn't happy about
processing the API doc comments for the affected function.

Also added a couple of other predefined macros used in Zephyr.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>