msm: mdss: Use heap instead of stack for panel_info in check var

If add new elements to the structure mdss_panel_info, there
are possibilities to run into build errors as local variable
of mdss_panel_info in function mdss_fb_check_var has huge
size which crossing the 2048 limit. Hence use heap instead
of stack for mdss_panel_info.

Change-Id: I1f07c2f00f5bf6cb494859a85108e3dab8775293
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>