drm/amd: Convert SDMA to use `amdgpu_ucode_ip_version_decode`

Simplifies the code so that all SDMA versions will get the firmware
name from `amdgpu_ucode_ip_version_decode`.

v2: squash in fix from Srinivasan

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>