drm/amdkfd: replace asic_name with amdgpu_asic_name

device_info->asic_name and amdgpu_asic_name[adev->asic_type] both
provide asic name strings, with the only difference being casing.
Remove asic_name from device_info and replace sysfs entry with lowercase
amdgpu_asic_name[]. Ensures string is null-terminated so that this
doesn't break if dev->node_props.name ever gets set anywhere else.

Signed-off-by: Graham Sider <Graham.Sider@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>