Fix OpenCL direct convolution

Fix OpenCL direct convolution

- The ARM DOT macro was using wrong variables for performing the dot
  product
- K0 could be a non power of 2 values when IFM was not a multiple of 16
- Refactor the test for direct convolution NHWC

Resolves COMPMID-4135, COMPMID-4155

Change-Id: I3a2dc89ef613ae20245cfc28e76ea36c55eaf81d
Signed-off-by: Gian Marco Iodice <gianmarco.iodice@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/4962
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: TeresaARM <teresa.charlinreyes@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>