Implement the .read handler for the NVM and Shadow RAM regions. This
enables user space to read a small chunk of the flash without needing the
overhead of creating a full snapshot.

Update the documentation for ice to detail which regions have direct read
support.
Signed-off-by: NJacob Keller <jacob.e.keller@intel.com>
Acked-by: NJakub Kicinski <kuba@kernel.org>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>