powerpc/iseries: remove the old viocons driver

This driver was declared obsolete over 2 years ago, the alternative
console driver for legacy iSeries (hvc_iseries) was made the default
over 1 year ago and this driver has been build broken for over 3
months, so remove it.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>