powerpc/pseries/dlpar: Search DRC index from ibm,drc-indexes for IO add

IO hotplug add event is handled in the user space with drmgr tool.
After the device is enabled, the user space uses /sys/kernel/dlpar
interface with “dt add index <drc_index>” to update the device tree.
The kernel interface (dlpar_hp_dt_add()) finds the parent node for
the specified ‘drc_index’ from ibm,drc-info property. The recent FW
provides this property from 2017 onwards. But KVM guest code in
some releases is still using the older SLOF firmware which has
ibm,drc-indexes property instead of ibm,drc-info.

If the ibm,drc-info is not available, this patch adds changes to
search ‘drc_index’ from the indexes array in ibm,drc-indexes
property to support old FW.

Fixes: 02b98ff4 ("powerpc/pseries/dlpar: Add device tree nodes for DLPAR IO add")
Reported-by: Kowshik Jois <kowsjois@linux.ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Tested-by: Amit Machhiwal <amachhiw@linux.ibm.com>
Reviewed-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250531235002.239213-1-haren@linux.ibm.com