drm/msm: Don't limit number of GPU commands

The maximum number is set to 10. But it couldn't cover. the required
number of GPU commands is increased significantly when upgrade
1080P resolution to 4K.
Change the driver to limit the number of GPU commands as long as there
is sufficient system memory

Change-Id: I797b644657c1ae0131b432183e7b735fd86e6dc0
Signed-off-by: Kasin Li <donglil@codeaurora.org>