vendorcode/eltan: Add vendor code for measured and verified boot

This patch contains the general files for the vendorcode/eltan that has
been uploaded recently:
- Add eltan directory to vendorcode
- Add documentation about the support in the vendorcode directories.
- Add the Makefile.inc and Kconfig for the vendorcode/eltan and
  vendorcode/eltan/security

BUG=N/A
TEST=Created verified binary and verify logging on Portwell PQ-M107

Change-Id: Ic1d5a21d40b6a31886777e8e9fe7b28c860f1a80
Signed-off-by: Frans Hendriks <fhendriks@eltan.com>
---
A Documentation/vendorcode/eltan/index.md
A Documentation/vendorcode/eltan/security.md
M src/vendorcode/Makefile.inc
A src/vendorcode/eltan/Kconfig
A src/vendorcode/eltan/Makefile.inc
A src/vendorcode/eltan/security/Kconfig
A src/vendorcode/eltan/security/Makefile.inc
7 files changed, 127 insertions(+), 0 deletions(-)