android: binder: Enable preemption for security_binder_transfer_file

Commit 5d226df4 ("selinux:
Revalidate invalid inode security labels") is incompatible with the
binder change to disable preemption while holding the global binder
lock, since it calls an API that might sleep while preemption is
disabled.  While upstream works on a proper solution for the binder
lock latency problem, we still need the preemption-disable changes in
order to maintain performance. Temporarily re-enable preemption
around security_binder_transfer_file until we obtain the correct fix
from android common.

Change-Id: Ieab87c4b3dbb882a3c8c6dce2c544aa619267d53
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>