powerpc/configs: add FADump awareness to skiroot_defconfig

FADump is supported on PowerNV platform. To fulfill this support, the
petitboot kernel must be FADump aware. Enable config PRESERVE_FA_DUMP
to make the petitboot kernel FADump aware.
Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/157062986936.23016.10146169203560084401.stgit@hbathini.in.ibm.com

arch/powerpc/configs/skiroot_defconfig

@@ -46,6 +46,7 @@ CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND=y
 CONFIG_CPU_IDLE=y
 CONFIG_HZ_100=y
 CONFIG_KEXEC=y
+CONFIG_PRESERVE_FA_DUMP=y
 CONFIG_IRQ_ALL_CPUS=y
 CONFIG_NUMA=y
 # CONFIG_COMPACTION is not set