powerpc/mpc5200: Make PSC UART driver update serial errors counters

This patch adds the capability to the mpc52xx-uart to report framing
errors, parity errors, breaks and overruns to userspace. These values
may be requested in userspace by using the ioctl TIOCGICOUNT.

Signed-off-by: René Bürgel <r.buergel@unicontrol.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>