spapr: Move DRC RTAS calls into spapr_drc.c

spapr: Move DRC RTAS calls into spapr_drc.c

Currently implementations of the RTAS calls related to DRCs are in
spapr_rtas.c.  They belong better in spapr_drc.c - that way they're closer
to related code, and we'll be able to make some more things local.

spapr_rtas.c was intended to contain the RTAS infrastructure and core calls
that don't belong anywhere else, not every RTAS implementation.

Code motion only.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Tested-by: Daniel Barboza <danielhb@linux.vnet.ibm.com>