[Tizen] Fix XWALK-1196

The application icons directory being used by xwalk on Tizen
is "Tizen mobile" specific and it is absent on Tizen generic
images causing application installation issues.

This patch provides a quick fix putting the code into "OS_TIZEN_MOBILE"
preprocessor guards, it should be re-considered further when
we know the appropriate place to store application icons on
Tizen IVI.

BUG=XWALK-1196