msm: msm_fb: Add remove function for platform driver for clean unloading

This adds a  remove function to platform driver structure so that
resources are released when driver is unloaded.

Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>

CC: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
CC: Tomi Valkeinen <tomi.valkeinen@ti.com>
CC: Stephen Boyd <sboyd@codeaurora.org>
CC: Jingoo Han <jg1.han@samsung.com>
CC: Rob Clark <robdclark@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>