gpu: nvgpu: zbc: disable activity only from ioctl

gpu: nvgpu: zbc: disable activity only from ioctl

Move the fifo engine activity disabling and wait-for-idle from the
lowest-level functions higher, into the ioctl path of zbc operations, so
that the sw initialization path wouldn't call them. During the init
path, the disable isn't necessary, and the code path could result in a
deadlock in the fifo runlist mutex.

Change-Id: Icf5c270ba29bc1c7f88874fba2d176d68e11278a
Signed-off-by: Konsta Holtta <kholtta@nvidia.com>
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/733668