hdata: Ensure the prd-label hbrt-code-image is prefixed
hdata: Ensure the prd-label hbrt-code-image is prefixed

Older versions of opal-prd (i.e. most of them shipped by distros)
expect the HBRT image to have the PRD label of "ibm,hbrt-code-image".
Commit c3bfa3209559 ("hdata: Fix reserved node label search") made
opal-prd check for both strings, but since opal-prd itself is the only
component interested in locating the hbrt-code-image we might as well
just add the prefix in firmware.

Cc: Vasant Hegde <a6d753843573f7bfed5075c1e875b0be8007a0ab@linux.vnet.ibm.com>
Signed-off-by: Oliver O'Halloran <3dfaff8fa6ae977f042064a112a6aac576279b9b@gmail.com>

shenki/skiboot,legoater/skiboot,open-power/skiboot,legoater/skiboot,open-power/skiboot,qemu/skiboot,qemu/skiboot,shenki/skiboot,qemu/skiboot,qemu/skiboot,legoater/skiboot,shenki/skiboot,open-power/skiboot,open-power/skiboot,legoater/skiboot,qemu/skiboot,open-power/skiboot,shenki/skiboot,shenki/skiboot,legoater/skiboot