drm/msm: Fix task dump in gpu recovery

The current recovery code gets a pointer to the task struct and does a
few things all within the rcu_read_lock. This puts constraints on the
types of gfp flags that can be used within the rcu lock. This patch
instead gets a reference to the task within the rcu lock and releases
the lock immediately, this way the task stays afloat until we need it and
we also get to use the desired gfp flags.

Signed-off-by: Sharat Masetty <smasetty@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>