RAS/AMD/FMPM: Safely handle saved records of various sizes

Currently, the size of the locally cached FRU record structures is
based on the module parameter "max_nr_entries".

This creates issues when restoring records if a user changes the
parameter.

If the number of entries is reduced, then old, larger records will not
be restored. The opportunity to take action on the saved data is missed.
Also, new records will be created and written to storage, even as the old
records remain in storage, resulting in wasted space.

If the number of entries is increased, then the length of the old,
smaller records will not be adjusted. This causes a checksum failure
which leads to the old record being cleared from storage. Again this
results in another missed opportunity for action on the saved data.

Allocate the temporary record with the maximum possible size based on
the current maximum number of supported entries (255). This allows the
ERST read operation to succeed if max_nr_entries has been increased.

Warn the user if a saved record exceeds the expected size and fail to
load the module. This allows the user to adjust the module parameter
without losing data or the opportunity to restore larger records.

Increase the size of a saved record up to the current max_rec_len. The
checksum will be recalculated, and the updated record will be written to
storage.

Fixes: 6f15e617cc99 ("RAS: Introduce a FRU memory poison manager")
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Muralidhara M K <muralidhara.mk@amd.com>
Link: https://lore.kernel.org/r/20240319113322.280096-3-yazen.ghannam@amd.com

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