drm/amdgpu: Fix SDMA engine reset with logical instance ID

This commit makes the following improvements to SDMA engine reset handling:

1. Clarifies in the function documentation that instance_id refers to a logical ID
2. Adds conversion from logical to physical instance ID before performing reset
   using GET_INST(SDMA0, instance_id) macro
3. Improves error messaging to indicate when a logical instance reset fails
4. Adds better code organization with blank lines for readability

The change ensures proper SDMA engine reset by using the correct physical
instance ID while maintaining the logical ID interface for callers.

V2: Remove harvest_config check and convert directly to physical instance (Lijo)

Suggested-by: Jonathan Kim <jonathan.kim@amd.com>
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>