cxlflash: Fix AFU version access/storage and add check

cxlflash: Fix AFU version access/storage and add check

The AFU version is stored as a non-terminated string of bytes within
a 64-bit little-endian register. Presently the value is read directly
(no MMIO accessor) and is stored in a buffer that is not big enough
to contain a NULL terminator. Additionally the version obtained is not
evaluated against a known value to prevent usage with unsupported AFUs.
All of these deficiencies can lead to a variety of problems.

To remedy, use the correct MMIO accessor to read the version value into
a null-terminated buffer and add a check to prevent an incompatible AFU
from being used with this driver.

Signed-off-by: Matthew R. Ochs <[email protected]>
Signed-off-by: Manoj N. Kumar <[email protected]>
Reviewed-by: Brian King <[email protected]>
Reviewed-by: Daniel Axtens <[email protected]>
Reviewed-by: Tomas Henzl <[email protected]>
Signed-off-by: James Bottomley <[email protected]>