msm: vidc: Never unload the firmware on certain platforms

On some platforms, we'd like to never unload the firmware so that we can
acheive lower latency on video start up.  This commit achieves that by
setting unload interval to an unreasonable time in the future if the
appropriate flag is set in the device tree.

Change-Id: I8960350a4bc0bdf244de575172399fc6ecc59ad9
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>