mem-cache: Add move assign and delete move constr of blk

mem-cache: Add move assign and delete move constr of blk

Some cache techniques may need to move a block's metadata information
into another block. This must have some limitations to avoid mistakes:
- The destination entry must be invalid, otherwise the replacement
  policy steps would be skipped.
- The source entry must be valid, otherwise there would be no point
  in moving their metadata contents.
- The entries locations (set, way, offset...) must not be moved, since
  they are fixed. The same principle is applied to the location specific
  variables, such as the replacement pointer

Why it would be used:
For example, when using compression, and a block goes from uncompressed
to compressed state due to an overwrite, after the tag lookup
(sequential access) it can be decided whether to store the new data in
the old location, or, since we might have already found the block's co-
allocatable blocks, move it to co-allocate.

Other examples of techniques that could use this functionality are
Skewed Compressed Caches, and ZCaches.

Change-Id: I96e4f8cc8c992c4b01f315251d1a75d51c28692c
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36575
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>