Do not depend on environment variables and use a kconfig variable
for defining the architecture.
In addition, remove the X86_32 variable, it just duplicates X86 for
not good reason, at least until start supporting MCUs with 64bit.
Change-Id: Ia001db81ed007e6a43f34506fed9be1345b88a4b
Signed-off-by: Anas Nashif <anas.nashif@intel.com>