[MTD] [NAND] nandsim: support random page read command

Commit 3d459559

 ("subpage read feature
as a way to improve performance") broke nandsim because nandsim does not
support the "random page read" NAND command. This patch adds
corresponding support.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>