msm_fb: display: no early suspend for writeback panel

Writeback panel is not real physical panel and no power consumption
concern, so it is removed from early suspend registration to avoid
open fb2 error during suspend/resume.

Change-Id: Ic61f69e069f2da8c73f2b5a13d103a2f20034d20
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>