pstore: Split pstore fragile flags

pstore: Split pstore fragile flags

This patch adds new PSTORE_FLAGS for each pstore type so that they can
be enabled separately.  This is a preparation for ongoing virtio-pstore
work to support those types flexibly.

The PSTORE_FLAGS_FRAGILE is changed to PSTORE_FLAGS_DMESG to preserve the
original behavior.

Cc: Anton Vorontsov <[email protected]>
Cc: Colin Cross <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Matt Fleming <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Namhyung Kim <[email protected]>
[kees: retained "FRAGILE" for now to make merges easier]
Signed-off-by: Kees Cook <[email protected]>