security: Used macros from compiler.h instead of __attribute__((...))

To increase compiler portability there is <linux/compiler.h> which
provides convenience macros for various gcc constructs.  Eg: __packed
for __attribute__((packed)).

This patch is part of a large task I've taken to clean the gcc
specific attributes and use the the macros instead.

Signed-off-by: Gideon Israel Dsouza <gidisrael@gmail.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>