Add IGEMM padding pointer testing
For LHS shapes which has more than one row, set the first row of data to be padding.
As this further increases the number of different test inputs this change also extends the caching mechanism to use an unordered map to store the generated test data, and uses a single object which encompasses all parameters used to generate test data
Signed-off-by: Emil Ohlsson emil.ohlsson@arm.com