powerpc: Update MPC5xxx and Xilinx Virtex maintainer entries

- Add git tree URLs
- Drop Sylvain from the 5xxx maintainers list.  He hasn't been active
  for a while now.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
1 file changed