drm/amd/amdgpu: Map ISP interrupts as generic IRQs

Map ISP IH interrupts to Linux generic IRQ for ISP driver to
handle the interrupts using MFD IORESOURCE_IRQ resource.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Pratap Nirujogi <pratap.nirujogi@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>