[u-boot-mgr]: Initial u-boot mgr hardening intf

Initial u-boot mgr to harden interface and usage. This
exposes method in D-Bus which other daemon can use to update
U-Boot environment variables, instead of directly using
fw_printenv  or fw_setenv tools.

Tested:
Verified able to query the ReadAll, Read and Write
method exposed in this interface.

Signed-off-by: Richard Marian Thomaiyar <richard.marian.thomaiyar@linux.intel.com>
Change-Id: I21772c8f30b7c68f5c9a2da3d44217ea2f533014
6 files changed