Define FREESMARTPHONE_GIT variable

FREESMARTPHONE_GIT used to be defined in bitbake.conf of 'openembedded-core' layer, but recently it was removed from there which broke several recipes in 'meta-oe' that still use it, such as:
 * recipes-support/serial-utils/pty-forward-native.bb
 * recipes-support/serial-utils/serial-forward_git.bb
 * recipes-support/vala-terminal/vala-terminal_git.bb
 * recipes-devtools/vala-dbus-binding-tool/vala-dbus-binding-tool_git.bb