IoTivity scons build update for Yocto

IoTivity scons build update for Yocto

* Added meta data for other architectures supported
by the Yocto toolchain. (For eg. we can now
build IoTivity for ARM/RaspberryPi)
* Added additional required compiler flags to be
used while building IoTivity for Yocto.
* Added new CROSS_COMPILE key to the construction
environment which can be used to build IoTivity's
external dependencies for Yocto. (For eg. gtest
uses autoconf, so CROSS_COMPILE gets passed in with
the --host switch)

Change-Id: Iad52c4fbc597abde32baf53205ddbd46e22f122b
Signed-off-by: Kishen Maloor <kishen.maloor@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/919
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Caiwen Zhang <caiwen.zhang@intel.com>
Reviewed-by: Erich Keane <erich.keane@intel.com>