pseries: Add more parameter validation in RTAS time of day functions

Currently, the RTAS time of day functions only partially validate the
number of parameters they receive and return.  Because of how the
parameters are used, this is unlikely to lead to a crash, but it's messy.

This patch adds the missing checks.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
