Force output shape to be correct for pooling operations

The avg_pool2d and max_pool2d operators trigger an error_if
statement if the output shape provided does not match the output
shape generated by the operation given the input arguments.

 * Add pseudocode for floor operation
 * Fixed type in RESCALE op

Signed-off-by: Matthew Haddon <matthew.haddon@arm.com>
Change-Id: I087faa331c30becc05719cd1261f436019dcdeb5