x86: iamcu: Add support for the IAMCU calling convention.

Add support for compilers conforming to the IAMCU calling convention
as documented by
https://github.com/hjl-tools/x86-psABI/wiki/iamcu-psABI-0.7.pdf


Change-Id: I6fd9d5bede0538b2049772e3850a5940c5dd911e
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
16 files changed