Add event groups demo to Zynq demo.

Add event groups demo to Zynq demo.
Add C implementations of some standard library functions to the Zynq demo to prevent the GCC libraries (which use floating point registers as scratch registers) being linked in.

git-svn-id: https://svn.code.sf.net/p/freertos/code/trunk@2199 1d2547de-c912-0410-9cb9-b8ca96c0e9e2