msm: mdss: modify dual-dsi interface swap implementation

In certain dual-dsi products it is possible to physically attach
left-panel on DSI1 interface and right-panel on DSI0 interface. This
particular configuration requires MDSS to swap its output going into
these two interfaces. Current implementation achieves this by swapping
pipes across two layer mixers (LMs) but that solution is not scalable
and optimum when used with source split. We can achieve the same results
by using crossbar located before MDSS interfaces which will allow ctl0
to send data to DSI1 and ctl1 to DSI0. This new implementation is
minimalist and scalable. Implement this new method by swapping interface
assigned to ctl path.

CRs-Fixed: 651286
Change-Id: I7a435f81bd42c197e2eb8655882da9352c091c09
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>
mdss: dsi: Don't make lack of reset GPIO a fatal failure yet

* mdss_dsi_request_gpios will make this a fatal failure later
  regardless.
* Also fix a error string copy paste error.

Change-Id: I7e49f5b547277a758e3b153dba1be43b46a1e774