Arm backend: Update gemma3n tests (#18159)

Updates the Gemma3n tests to follow the common test structure
Fixes for TOSA/VGF backend of Gemma3n layer tests

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils
@Sebastian-Larsson @robell

Signed-off-by: Adrian Lundell <adrian.lundell@arm.com>
Co-authored-by: Adrian Lundell <adrian.lundell@arm.com>

Author: xingguo01