Use a dedicated copy of the current power state since
we may have to adjust it on the fly.

v2: fix up redundant state sets
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

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

This adds dpm support for btc asics.  This includes:
- clockgating
- dynamic engine clock scaling
- dynamic memory clock scaling
- dynamic voltage scaling
- dynamic pcie gen1/gen2 switching (requires additional acpi support)

Set radeon.dpm=1 to enable.

v2: reduce stack usage
v3: attempt to fix state enable
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>