openpower:dreport: add core and BMC generated dump file list to the BMC dump

List all the dump file names with path and append the output file to
BMC dump.

Tested
[core files]

[BMC dumps]
/var/lib/phosphor-debug-collector/dumps/23/BMCDUMP.13E8CEX.00000023.20220328231804
/var/lib/phosphor-debug-collector/dumps/24/BMCDUMP.13E8CEX.00000024.20220329045155

[Hardware dumps]

[Hostboot dumps]

[SBE dumps]

Signed-off-by: Marri Devender Rao <devenrao@in.ibm.com>
Change-Id: Iac5f0e6d542ba1fa5b18b5c9399ee7537e05e274