Add basic support for ST m41t93 SPI RTCs.  Tested with factory-new and
with "run-in" species with and without backup batteries.
Signed-off-by: NNikolaus Voss <n.voss@weinmann.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>