drm/amdgpu/umsch: tidy up the ucode name string handling

Make the constant parts of the name part of the string
we pass to amdgpu_ucode_request().  Only the version
number varies from IP to IP.

Reviewed-by: Saleemkhan Jamadar <saleemkhan.jamadar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Lang Yu <Lang.Yu@amd.com>