drm/amdgpu/powerplay: partial revert of endian fixes

This fixes a warning on big endian. Bitfields need to
be handled properly.

Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>