gpu: nvgpu: enable powergate always while releasing debug session

gpu: nvgpu: enable powergate always while releasing debug session

Currently, while releasing the debug session we enable powergate
only if a channel is bound to session

If a session has no channel bound to it, and has powergate
disabled, then we do not enable powergate when that session
is closed

Fix this by calling dbg_set_powergate(POWERGATE_ENABLE) always
while releasing the session

Refcounting and sanity checks in dbg_set_powergate() will take
care of situation if powergate was not disabled by the session
in first place

Bug 1679372

Change-Id: I4e027393c611d3e8ab4f20e195f31871086da736
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/796999
cherry picked from commit 671dff8cb0605f865c5da32bd889e2a6fcf133fe)
Reviewed-on: http://git-master/r/801986
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>