openpower:dreport: Save badPEL file in dump

The last invalid/corrupt PEL the host sent down to the BMC is saved in
/var/lib/phosphor-logging/extensions/pels/badPEL.  Save it in a dump if
it exists so we can get the contents when it happens in the field.

Tested:
~/BMCDUMP.SIMP10R.00000000.20221012205429_out/archive$ ls -l badPEL
-rw-r--r--. 1 spinler spinler 5599 Oct 12 15:54 badPEL

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Id6052d5c4c052860e978314e541d4a1b978ee615