Remove AMD Agesa requirement for standard include files

Remove AMD Agesa requirement for standard include files

This change modifies Makefile.inc to add the -nostdinc flag to the default
CFLAGS value and removes the test for non-AMD Agesa builds.  Other code is
added to the gcc-intrin.h file in the Agesa Include folder to make the
requirement for the standard includes obsolete from the Agesa perspective.

Signed-off-by: Frank Vibrans <frank.vibrans@amd.com>
Acked-by: Marc Jones <marcj303@gmail.com>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@6555 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1