msm: mdss: Clean up histogram software state when FB device is released

When framebuffer device is released, the software state for the histograms
attached to that FB remains unchanged. During the release of FB resources,
the histogram state should be reset back to idle. This change adds that
support.

Change-Id: I0e9adcb5b98b8ea219c0bd5b0afa791f5820dc95
Signed-off-by: Benet Clark <benetc@codeaurora.org>