ppc/xics: Replace "icp" with "xics" in most places

ppc/xics: Replace "icp" with "xics" in most places

The "ICP" is a different object than the "XICS". For historical reasons,
we have a number of places where we name a variable "icp" while it contains
a XICSState pointer. There *is* an ICPState structure too so this makes
the code really confusing.

This is a mechanical replacement of all those instances to use the name
"xics" instead. There should be no functional change.

Signed-off-by: Benjamin Herrenschmidt <[email protected]>
[spapr_cpu_init has been moved to spapr_cpu_core.c, change there]
Signed-off-by: Nikunj A Dadhania <[email protected]>
Reviewed-by: David Gibson <[email protected]>
Signed-off-by: David Gibson <[email protected]>