drm/radeon: add initial ucode loading for CIK (v5)

Currently the driver required 6 sets of ucode:
1. pfp - pre-fetch parser, part of the GFX CP
2. me - micro engine, part of the GFX CP
3. ce - constant engine, part of the GFX CP
4. rlc - interrupt, etc. controller
5. mc - memory controller (discrete cards only)
6. mec - compute engines, part of Compute CP

V2: add documentation
V3: update MC ucode
V4: rebase
V5: update mc ucode

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>