This adds dpm support for btc asics. This includes:
- dynamic engine clock scaling
- dynamic memory clock scaling
- dynamic voltage scaling
- dynamic pcie gen switching

Set radeon.dpm=1 to enable.

v2: remove unused radeon_atombios.c changes,
    make missing smc ucode non-fatal
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>