drm/amd/amdgpu: fix the HDP LS/DS/SD programming

confirmed that IPH_MEM_POWER_CTRL_EN and RC_MEM_POWER_CTRL_EN
have to be set for SRAM LS/DS/SD

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Likun Gao <Likun.Gao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>