Increase app IRAM to 4KB + Minor Fix to HDL + Test bench updates

• Increases application IRAM to 4KB (+ensures correct size is assigned to application DRAM so it matches linker file .bss section - LENGTH = 4096)
• Minor fixes to HDL following introduction of generics for IRAM/DRAM application sizes
• Fixes to allow top level test bench (note we get asserts when running it - to be discussed)

See commits for more details