drm/msm/adreno: Defer enabling runpm until hw_init()

To avoid preventing the display from coming up before the rootfs is
mounted, without resorting to packing fw in the initrd, the GPU has
this limbo state where the device is probed, but we aren't ready to
start sending commands to it.  This is particularly problematic for
a6xx, since the GMU (which requires fw to be loaded) is the one that
is controlling the power/clk/icc votes.

So defer enabling runpm until we are ready to call gpu->hw_init(),
as that is a point where we know we have all the needed fw and are
ready to start sending commands to the coproc's.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/489337/
Link: https://lore.kernel.org/r/20220613182036.2567963-1-robdclark@gmail.com