drm/amd/powerplay: add interface to allocate memory pool (v2)

This patch adds interface to allocate memory pool for smu.
This memory pool will be used for SMC use and msg SetSystemVirtualDramAddr and
DramLogSetDramAddr can notify it changed.

v2: add detailed info to describe this function

Signed-off-by: Huang Rui <ray.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>